California Plumbing Code

Part I

501.0 General.The regulations of this chapter shall govern theconstruction, location, and installation of fuel-burning and other water heaters heating potablewater, together with all chimneys, vents, and theirconnectors. The minimum capacity for water heatersshall be in accordance with the first hour rating listedin Table 5-1. All design, construction, and work-manship shall be in conformity with acceptedengineering practices, manufacturer’s installationinstructions, and applicable standards and shall be ofsuch character as to secure the results sought to beobtained by this code. No water heater shall behereinafter installed that does not comply in allrespects with the type and model of each size thereofapproved by the Authority Having Jurisdiction. Alist of accepted gas equipment standards is includedin Table 14-1.

502.0 Definitions.502.1 Appliance Categorized Vent Diameter/Area.The minimum vent area/diameter permissible forCategory I appliances to maintain a nonpositive ventstatic pressure when tested in accordance withnationally recognized standards. [NFPA 54:3.3.7]502.2 Chimney. (See also Gas Vent, and VentingSystem.) One or more passageways, vertical ornearly so, for conveying flue or vent gases to theoutside atmosphere. [NFPA 54: 3.3.17]502.3 Chimney, Factory-Built. A chimney composedof listed factory-built components assembled inaccordance with the terms of listing to form thecompleted chimney. [NFPA 54: 3.3.17.2]502.4 Chimney, Masonry. A field-constructedchimney of solid masonry units, bricks, stones, listedmasonry chimney units, or reinforced portlandcement concrete, lined with suitable chimney flueliners. [NFPA 54: 3.3.17.3]

502.5 Chimney, Metal. A field-constructed chimneyof metal. [NFPA 54: 3.3.17.4]502.6 Combustible Material. As pertaining tomaterials adjacent to or in contact with heat-producingappliances, vent connectors, gas vents, chimneys, steamand hot water pipes, and warm air ducts, shall meanmaterials made of or surfaced with wood, compressedpaper, plant fibers, or other materials that are capableof being ignited and burned. Such material shall beconsidered combustible even though flame-proofed,fire-retardant treated, or plastered. [NFPA 54: 3.3.65.1]502.7 Direct-Vent Appliances. Appliances that areconstructed and installed so that all air for combustionis derived directly from the outside atmosphere andall flue gases are discharged to the outsideatmosphere. [NFPA 54: 3.3.6.3]502.8 Flue Collar. That portion of an appliancedesigned for the attachment of a draft hood, ventconnector, or venting system. [NFPA 54: 3.3.45]502.9 Gas Vent, Type B. A vent for venting-listedgas appliances with draft hoods and other Category Iappliances listed for use with Type B gas vents.[NFPA 54: 3.3.105.2.2]502.10 Gas Vent, Type L. A vent for ventingappliances listed for use with Type L vents andappliances listed for use with Type B gas vents.[NFPA 54: 3.3.105.2.4]502.11 Indirect-Fired Water Heater. A water heaterconsisting of a storage tank equipped with an internalor external heat exchanger used to transfer heat froman external source to heat potable water. The storagetank may contain heated potable water or watersupplied from an external source, such as a boiler.502.12 Vent. A passageway used to convey flue gasesfrom gas utilization equipment or their vent connectorsto the outside atmosphere. [NFPA 54: 3.3.105]502.13 Vent Connector. The pipe or duct thatconnects a fuel-gas-burning appliance to a vent orchimney. [NFPA 54: 3.3.106]

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CHAPTER 5WATER HEATERS

TABLE 5-11 FIRST HOUR RATING

Number of Bathrooms 1 to 1.5 2 to 2.5 3 to 3.5Number of Bedrooms 1 2 3 2 3 4 5 3 4 5 6First Hour Rating,2 Gallons 42 54 54 54 67 67 80 67 80 80 80

Note:1 The first hour rating is found on the “Energy Guide” lable.2 Non-storage and solar water heaters shall be sized to meet the appropriate first hour rating as shown in the table.

502.14 Venting System . A continuous openpassageway from the flue collar or draft hood of agas-burning appliance to the outside atmosphere forthe purpose of removing flue or vent gases. [NFPA54: 3.3.98.7]502.15 Water Heater. An appliance for supplying hotwater for domestic or commercial purposes. [NFPA54: 3.3.55.7]

503.0 Permits.It shall be unlawful for any person to install, remove, orreplace or cause to be installed, removed, or replacedany water heater without first obtaining a permit fromthe Authority Having Jurisdiction to do so.

504.0 Inspection.504.1 Inspection of Chimneys or Vents. Thisinspection shall be made after all chimneys, vents, orparts thereof, authorized by the permit, have beeninstalled and before any such vent or part thereof hasbeen covered or concealed.504.2 Final Water Heater Inspection. Thisinspection shall be made after all work authorized bythe permit has been installed. The Authority HavingJurisdiction will make such inspection as deemednecessary to be assured that the work has beeninstalled in accordance with the intent of this code.No equipment or part thereof shall be covered orconcealed until the same has been inspected andapproved by the Authority Having Jurisdiction.

505.0 Water Heater Requirements.505.1 Location. Water heater installations in bed-rooms and bathrooms shall comply with one of thefollowing [NFPA 54: 10.28.1]:(1) Fuel-burning water heaters may be installed in a

closet located in the bedroom or bathroomprovided the closet is equipped with a listed,gasketed door assembly and a listed self-closingdevice. The self-closing door assembly shallmeet the requirements of Section 505.1.1. Thedoor assembly shall be installed with a thresholdand bottom door seal and shall meet therequirements of Section 505.1.2. All combustionair for such installations shall be obtained fromthe outdoors in accordance with Section 507.4.The closet shall be for the exclusive use of thewater heater.

(2) Water heater shall be of the direct vent type.[NFPA 54:10.28.1.2]505.1.1 Self-Closing Doors. Self-closing doorsshall swing easily and freely and shall be

equipped with a self-closing device to cause thedoor to close and latch each time it is opened.The closing mechanism shall not have a hold-open feature. [NFPA 80:2-1.4.1]505.1.2 Gasketing. Gasketing on gasketed doorsor frames shall be furnished only in accordancewith the published listings of the doors, frame,or gasketing material manufacturer.Exception: Where acceptable to the AuthorityHaving Jurisdiction, gasketing of noncombustibleor limited-combustible material (see NFPA 220)Standard on Types of Building Construction)shall be permitted to be applied to the frame,provided closing and latching of the door are notinhibited. [NFPA 80:2-4.8]

505.2 Water heaters of other than the direct-venttype shall be located as close as practical to thechimney or gas vent. [NFPA 54:9.28.1.2]505.3 Clearance.

505.3.1 The clearances shall not be such as tointerfere with combustion air, draft hood clearanceand relief, and accessibility for servicing. Listedwater heaters shall be installed in accordance withtheir listings and the manufacturers' instructions.[NFPA 54:10.28.2.1]505.3.2 Unlisted water heaters shall be installedwith a clearance of 12 inches (300 mm) on all sidesand rear. Combustible floors under unlistedwater heaters shall be protected in an approvedmanner. [NFPA 54:10.28.2.2]

505.4 Pressure-Limiting Devices. A water heaterinstallation shall be provided with overpressureprotection by means of an approved, listed device,installed in accordance with the terms of its listing andthe manufacturer's instructions. [NFPA 54: 10.28.3]505.5 Temperature-Limiting Devices. A waterheater installation or a hot water storage vesselinstallation shall be provided with overtemperatureprotection by means of an approved, listed deviceinstalled in accordance with the terms of its listing andthe manufacturer's instructions. [NFPA 54: 10.28.4]505.6 Temperature, Pressure, and Vacuum ReliefDevices. The installation of temperature, pressure,and vacuum relief devices or combinations thereof,and automatic gas shutoff devices, shall be installedin accordance with the terms of their listings and themanufacturers' instructions. A shutoff valve shall notbe placed between the relief valve and the waterheater or on discharge pipes between such valvesand the atmosphere. The hourly Btu dischargecapacity or the rated steam relief capacity of thedevice shall not be less than the input rating of thewater heater. [NFPA 54: 10.28.5]

2007 CALIFORNIA PLUMBING CODE

54

502.14 – 505.6

506.0 Oil-Burning and Other Water Heaters.506.1 Water heaters deriving heat from fuels or typesof energy other than gas shall be constructed andinstalled in accordance with approved standards.Vents or chimneys for such appliances shall beapproved types. An adequate supply of air forcombustion and for adequate ventilation of heaterrooms or compartments shall be provided. Each suchappliance shall be installed in a location approved bythe Authority Having Jurisdiction and local and statefire-prevention agencies.506.2 All storage-type water heaters and hot waterboilers deriving heat from fuels or types of energyother than gas, shall be provided with, in addition tothe primary temperature controls, an overtemperaturesafety protection device constructed, listed, andinstalled in accordance with nationally recognizedapplicable standards for such devices and acombination temperature and pressure-relief valve.506.3 Oil-fired water heaters shall be installed inaccordance with NFPA 31, Standard for the Installationof Oil-Burning Equipment.506.4 Indirect-Fired Water Heaters

506.4.1 Indirect-fired water heaters shallconform to applicable sections of the ASMEBoiler and Pressure Vessel Code, or to one of theother applicable standards shown in Table 14-1.Each water heater shall bear a label inaccordance with ASME requirements, or anapproved testing agency, certifying and attestingthat such equipment has been tested andinspected and meets the requirements of theapplicable standards or code.506.4.2 Indirect-fired water heater that incor-porate a single-wall heat exchanger shall meetall of the following requirements:(1) Connected to a low-pressure hot water

boiler limited to a maximum of 30 psig byan approved safety or relief valve.

(2) Heater transfer medium is either potablewater or contains fluids having a toxicityrating or Class of 1.

(3) Bear a label with the word “Caution,”followed by the following statements:(a) The heat-transfer medium must be

water or other nontoxic fluid having atoxic rating or Class of 1 as listed inClinical Toxicology of CommercialProducts, 5th edition.

(b) The pressure of the heat-transfermedium must be limited to a maximumof 30 psig by an approved safety orrelief valve.Note: The word “Caution” and thestatements in letters having a minimumuppercase height of 0.120 inch (3.05mm). The minimum vertical spacingbetween lines of type shall be 0.046 inch(1.17 mm). Lowercase letters shall be

compatible with the uppercase lettersize specification.

507.0 Air for Combustion and Ventilation.507.1 General.

507.1.1 Air for combustion, ventilation, anddilution of flue gases for gas utilization equipmentinstalled in buildings shall be obtained byapplication of one of the methods covered inSections 507.2.1 through 507.7. Gas utilizationequipment of other than natural draft andCategory I vented appliances shall be providedwith combustion, ventilation, and dilution air inaccordance with the equipment manufacturer'sinstructions. Where infiltration does not providethe necessary air, outdoor air shall be introduced inaccordance with methods covered in Sections 507.4through 507.7. [NFPA 54:9.3.1.1]Exception No. 1: This provision shall notapply to direct-vent appliances. [NFPA 54-2002:8.3.1.1]Exception No. 2: Type 1 clothes dryers thatare provided with make-up air inaccordance with section NFPA 54:10.4.3.507.1.1.1 Clothes Dryer. A device used todry wet laundry by means of heat derivedfrom the combustion of fuel gases. [NFPA54:3.3.18]507.1.1.2 Clothes Dryer, Type 1. Primarilyused in family living environment. Mayor may not be coin-operated for public use.[NFPA 54:3.3.18.1]507.1.1.3 Exhausting to the Outdoors.Type 1 and Type 2 clothes dryers shall beexhausted to the outside air. [NFPA 54:10.4.2]507.1.1.4 Provisions for Make-Up Air.Make-up air shall be provided for Type 1clothes dryers in accordance with themanufacturers’ installation instructions.[NFPA 54:10.4.3.1]

507.1.2 Gas appliances of other than naturaldraft design and other than Category I ventedappliances shall be provided with combustion,ventilation, and dilution air in accordance withthe appliance manufacturer's instructions.[NFPA 54:9.3.1.2]507.1.3Where used, a draft hood or a barometricdraft regulator shall be installed in the sameroom or enclosure as the equipment served so asto prevent any difference in pressure between thehood or regulator and the combustion air supply.[NFPA 54:9.3.1.4]507.1.4 Makeup air requirements for theoperation of exhaust fans, kitchen ventilationsystems, clothes dryers, and fireplaces shall beconsidered in determining the adequacy of a

WATER HEATERS 506.0 – 507.1

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space to provide combustion air requirements.[NFPA 54:9.3.1.5]

507.2 Indoor Combustion Air. The requiredvolume of indoor air shall be determined inaccordance with Sections 507.2.1 or 507.2.2 exceptthat where the air infiltration rate is known to be lessthan 0.40 ACH, Section 507.2.2 shall be used. Thetotal required volume shall be the sum of therequired volume calculated for all appliances locatedwithin the space. Rooms communicating directlywith the space in which the appliances are installedthrough openings not furnished with doors, andthrough combustion air openings sized and locatedin accordance with Section 507.3 are considered apart of the required volume. [NFPA 54:9.3.2]

507.2.1 Standard Method.The minimumrequired volume shall be 50 cubic feet per 1,000Btu/hour (4.8 m3/kW). [NFPA 54:9.3.2.1]507.2.2 Known Air Infiltration Rate Method.Where the air infiltration rate of a structure isknown, the minimum required volume shall bedetermined as follows [NFPA 54:9.3.2.2]:(1) For appliances having other than fan-assisted,combustion systems: calculate using Equation5-1 but no smaller than 35 cubic feet per 1,000Btu/hour (3.4 m3/kW). [NFPA 54:9.3.2.2(1)](2) For fan-assisted combustion system appliances,calculate using Equation 5-2 but no smallerthan 25 cubic feet per 1,000 Btu/hour (2.4 m3/kW).[NFPA 54:9.3.2.2(2)]

Equation 5-1:Required Volume other > ( 21 ft3 /ACH) x ( Iother/1,000 Btu/h)Equation 5-2:Required Volume fan > ( 15 ft3 /ACH) x ( Ifan/1,000 Btu/h)

Where:Iother = All Appliances other than Fan-Assisted

Input in Btu/hourIfan = Fan-Assisted Appliance Input in Btu/hourACH = Air Change per Hour (Percent of volume of

space exchanged per hour, expressed as adecimal)

507.3 Indoor Opening Size and Location.Openings used to connect indoor spaces shall besized and located in accordance with the following[NFPA 54:9.3.2.3]:

(1) Combining spaces on the same story. Eachopening shall have a minimum free area of 1in.2/1,000 Btu/h (2200 mm2/kW) of the totalinput rating of all gas utilization equipmentin the space, but not less than 100 in.2(0.06 m2). One opening shall commence

within 12 inches (300 mm) of the top, and oneopening shall commence within 12 inches(300 mm) of the bottom of the enclosure[see Figure 5-12]. The minimum dimension ofair openings shall be not less than 3 inches(80mm). [NFPA 54:9.3.2.3(1)]

(2) Combining spaces in different stories. Thevolumes of spaces in different stories shall beconsidered as communicating spaces wheresuch spaces are connected by one or moreopenings in doors or floors having a totalminimum free area of 2 in.2/1,000 Btu/h(4,400 mm2/kW) of total input rating of allgas utilization equipment. [NFPA 54:8.3.2.3(2)]

507.4 Outdoor Combustion Air. Outdoor combustionair shall be provided through opening(s) to theoutdoors in accordance with methods Sections 507.4.1or 507.4.2. The minimum dimension of air openingsshall not be less than 3 inches (80mm). [NFPA 54:9.3.3]

507.4.1 Two Permanent Openings Method:Two permanent openings, one commencingwithin 12 inches (300 mm) of the top and onecommencing within 12 inches (300 mm) of thebottom of the enclosure shall be provided. Theopenings shall communicate directly, or byducts, with the outdoors or spaces that freelycommunicate with the outdoors as follows. [SeeFigure 5-7.][NFPA 54:9.3.3.1](1) Where directly communicating with the

outdoors or where communicating to theoutdoors through vertical ducts, eachopening shall have a minimum free area of 1in.2/4000 Btu/h (550 mm2/kW) of total inputrating of all equipment in the enclosure. [SeeFigures 5-8 and 5-9.] [NFPA 54:9.3.3.1(1)]

(2) Where communicating with the outdoorsthrough horizontal ducts, each opening shallhave a minimum free area of 1 in.2/2,000Btu/h (1,100 mm2/kW) of total input ratingof all equipment in the enclosure. [SeeFigure 5-10] [NFPA 54:9.3.3.1(2)]

507.4.2 One Permanent Opening Method: Onepermanent opening, commencing within 12inches (300 mm) of the top of the enclosure, shallbe provided. The equipment shall have clearancesof at least 1 inch (25 mm) from the sides and backand 6 inches (160 mm) from the front of theappliance. The opening shall directlycommunicate with the outdoors or shallcommunicate through a vertical or horizontalduct to the outdoors or spaces that freelycommunicate with the outdoors [seeFigure 5-11] and shall have aminimum free area ofthe following [NFPA 54:9.3.3.2]:(1) 1 in.2/3000 Btu/h (700 mm2/kW) of the


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507.1 – 507.4


57

total input rating of all equipment located inthe enclosure, and [NFPA 54:9.3.3.2(1)]

(2) Not less than the sum of the areas of all ventconnectors in the space. [NFPA 54: 9.3.3.2(2)]

507.5 Combination Indoor and Outdoor Com-bustion Air. The use of a combination of indoor andoutdoor combustion air shall be in accordance withSections 507.5.1, 507.5.2 and 507.5.3 [see examplecalculation in NFPA 54 Annex J and this chapter –Part II] [NFPA 54:9.3.4].

507.5.1 Indoor Openings. Where used,openings connecting the interior spaces shallcomply with Section 507.3. [NFPA 54:9.3.4(1)]507.5.2 Outdoor openings shall be located inaccordance with Sections 507.4.1 or 507.4.2.[NFPA 54:9.3.4(2)]507.5.3 Outdoor Openings Size. The outdooropenings size shall be calculated in accordancewith the following [NFPA 54:9.3.4(3)]:(1) The ratio of interior spaces shall be the

available volume of all communicating spacesdivided by the required volume.

(2) The outdoor size reduction factor shall be 1minus the ratio of interior spaces.

(3) The minimum size of outdoor openingsshall be the full size of outdoor openingscalculated in accordance with Sections507.4.1 or 507.4.2, multiplied by thereduction factor. The minimum dimensionof air openings shall not be less than 3 inches(80mm). [NFPA 54:8.3.4(3)(c)]

507.6 Engineered Installations. Engineeredcombustion air installations shall provide anadequate supply of combustion, ventilation, anddilution air and shall be approved by the AuthorityHaving Jurisdiction. [NFPA 54: 9.3.5]507.7 Mechanical Combustion Air Supply. Whereall combustion air is provided by a mechanical airsupply system, the combustion air shall be suppliedfrom outdoors at the minimum rate of 0.35 feet3/minper 1,000 Btu/h (0.034 m3/min per kW) for allappliances located within the space.

507.7.1 Where exhaust fans are installed,additional air shall be provided to replace theexhausted air. [NFPA 54:9.3.6.1]507.7.2 Each of the appliances served shall beinterlocked to the mechanical air supplysystem to prevent main burner operationwhere the mechanical air supply system is notin operation. [NFPA 54:9.3.6.2]507.7.3 Where combustion air is provided bythe building's mechanical ventilation system, thesystem shall provide the specified combustionair rate in addition to the required ventilationair. [NFPA 54: 9.3.6.3]

507.8 Louvers Grilles and Screens.(A) Louvers and Grilles. The required size of

openings for combustion, ventilation,anddilution air shall be based on the net free areaof each opening. Where the free area througha design of louver or grille is known, it shallbe used in calculating the size openingrequired to provide the free area specified.Where the design and free area are notknown, it shall be assumed that wood louverswill have 25 percent free area and metallouvers and grilles will have 75 percent freearea. Nonmotorized louvers and grillesshall be fixed in the open position. [NFPA54:9.3.7.1]

(B) Screens. Screens shall not be smaller than1/4-inch mesh. [NFPA 54:9.3.7.2]

(C) Motorized louvers shall be interlocked withthe equipment so they are proven in the fullopen position prior to main burner ignitionand during main burner operation. Meansshall be provided to prevent the main burnerfrom igniting should the louver fail to openduring burner start-up and to shut down themain burner if the louvers close duringburner operation. [NFPA 54: 9.3.7.3]

507.9 Combustion Air Ducts. Combustion air ductsshall comply with the following:

(1) Ducts shall be of galvanized steel or amaterial having equivalent corrosion resis-tance, strength, and rigidity. [NFPA 54:9.3.8.1]Exception: Within dwelling units, un-obstructed stud and joist spaces shall not beprohibited from conveying combustion air,provided that not more than one fireblock isremoved.

(2) Ducts shall terminate in an unobstructedspace, allowing free movement of combustionair to the appliances. [NFPA 54:9.3.8.2]

(3) Ducts shall serve a single space.[NFPA54:9.3.8.3]

(4) Ducts shall not service both upper andlower combustion air openings where bothsuch openings are used. The separationbetween ducts serving upper and lowercombustion air openings shall be maintainedto the source of combustion air. [NFPA54:9.3.8.4]

(5) Ducts shall not be screened where termi-nating in an attic space. [NFPA 54:9.3.8.5]

(6) Intakes for combustion air ducts locatedexterior to the building shall have the lowestside of the combustion air intake openingslocated at least 12 inches (300 mm) verticallyfrom the adjoining grade level.

(7) Horizontal upper combustion air ducts shallnot slope downward toward the source ofcombustion air. [NFPA 54:9.3.8.6]

(8) The remaining space surrounding achimney liner, gas vent, special gas vent, orplastic piping installed within a masonrychimney flue, metal or factory-builtchimney, shall not be used to supplycombustion air [NFPA 54:9.3.8.7], unless it islisted and shown in the manufacturer'sinstallation instructions.

508.0 Other Water Heater Installation Requirements.508.1 The Authority Having Jurisdiction shall havethe authority to require the use of an approveddielectric insulator on the water piping connections ofwater heaters and related water heating equipment.508.2 Protection from Seismic Damage. In seismicdesign categories C, D, E, and F water heaters shallbe anchored or strapped to resist horizontaldisplacement due to earthquake motion. Strappingshall be at points within the upper one third (1/3)and lower one-third (1/3) of its vertical dimensions.At the lower point, a minimum distance of four (4)inches (102 mm) shall be maintained above thecontrols with the strapping.

508.2.1 [HCD 1, HCD 2, and SFM] Protectionfrom seismic damage.* * * Water heaters shall beanchored to resist horizontal displacement due toearthquake motion. Strapping shall be at pointswithin the upper one third (1/3) and lower one-third(1/3) of its vertical dimensions. At the lower point, aminimum distance of four (4) inches (102 mm) shallbe maintained above the controls with the strapping.

Note: [HCD 1 & HCD 2] Reference Health and SafetyCode Section 19211(a) which addresses new, replacement,and existing water heaters.Note: [SFM] The applicable subsection of Health andSafety Code section 19211(a) which addresses new,replacement, and existing water heaters is repeated herefor clarity and reads as follows:

Section 19211(a) Notwithstanding Section 19100, allnew and replacement water heaters, and all existingresidential water heaters shall be braced, anchored, orstrapped to resist falling or horizontal displacement due toearthquake motion. At a minimum, any water heater shallbe secured in accordance with the California PlumbingCode, or modifications made thereto by a city county, orcity and county pursuant to Section 17958.5.508.3 A water heater supported from the groundshall rest on level concrete or other approved baseextending not less than three (3) inches (76 mm)above the adjoining ground level.

508.4When a water heater is located in an attic, attic-ceiling assembly, floor-ceiling assembly, or floor-subfloor assembly where damage may result from aleaking water heater, a watertight pan of corrosion-resistant materials shall be installed beneath thewater heater with a minimum three-quarter (3/4)inch (20 mm) diameter drain to an approved location.508.5 Relief Valve Discharge.Discharge from a relief valve into a water heater panshall be prohibited.508.6 Added or Converted Equipment.When addi-tional or replacement equipment is installed or anappliance is converted to gas from another fuel, thelocation in which the equipment is to be operated shallbe checked to verify the following [NFPA 54:9.1.2]:

508.6.1 Air for combustion and ventilation isprovided where required, in accordance with theprovisions of Section 507.0. Where existingfacilities are not adequate, they shall beupgraded to Section 507.0 specifications [NFPA54:9.1.2(1)].508.6.2 The installation components and equip-ment meet the clearances to combustible materialprovisions of NFPA 54:9.2.2. It shall be deter-mined that the installation and operation ofthe additional or replacement equipment doesnot render the remaining equipment unsafe forcontinued operation. [NFPA 54:9.1.2(2)](The following reference was extracted from NFPA 54.)9.2.2 Clearance to Combustible Materials. Gasutilization equipment and their vent connectors shall beinstalled with clearances from combustible material sotheir operation will not create a hazard to persons orproperty. Minimum clearances between combustiblewalls and the back and sides of various conventionaltypes of equipment and their vent connectors arespecified in Chapters 9 and 10. (Reference can also bemade to NFPA 211, Standard for Chimneys, Fireplaces,Vents, and Solid Fuel-Burning Appliances.)508.6.3 The venting system is constructed andsized in accordance with the provisions of thischapter. Where the existing venting system isnot adequate, it shall be upgraded to complywith this chapter. [NFPA 54: 9.1.2(3)]

508.7 Types of Gases. It shall be determinedwhether the gas-utilization equipment has beendesigned for use with the gas to which it will beconnected. No attempt shall be made to convert theequipment from the gas specified on the rating platefor use with a different gas without consulting theinstallation instructions, the serving gas supplier, orthe equipment manufacturer for complete instruc-tions. [NFPA 54: 9.1.3]


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507.4 – 508.7

508.8 Safety Shutoff Devices for Unlisted LP-GasEquipment Used Indoors. Unlisted gas utilizationequipment for use with undiluted liquefiedpetroleum gases and installed indoors shall beequipped with safety shutoff devices of the completeshutoff type. [NFPA 54: 9.1.4]508.9 Use of Air or Oxygen Under Pressure. Whereair or oxygen under pressure is used in connection withthe gas supply, effective means such as a back-pressureregulator and relief valve shall be provided to preventair or oxygen from passing back into the gas piping.Where oxygen is used, installation shall be in accordancewith NFPA 51, Standard for the Design and Installation ofOxygen-Fuel Gas Systems for Welding, Cutting, and AlliedProcesses. [NFPA 54: 9.1.5]508.10 Protection of Gas Equipment from Fumesor Gases Other than Products of Combustion.Non-direct vent-type gas appliances installed inbeauty shops, barbershops, or other facilities wherechemicals that generate corrosive or flammableproducts such as aerosol sprays are routinely usedshall be located in an equipment room separate orpartitioned off from other areas with provisions forcombustion and dilution air from outdoors. Directvent equipment shall be installed in accordance withthe appliance manufacturer's installation instructions.[NFPA 54: 9.1.6.2]508.11 Process Air. In addition to air needed forcombustion in commercial or industrial processes,process air shall be provided as required for coolingof equipment or material, controlling dew point,heating, drying, oxidation, dilution, safety exhaust,odor control, air for compressors, and for comfortand proper working conditions for personnel.[NFPA 54: 9.1.7]508.12 Building Structural Members.

508.12.1 Structural members of a building shallnot pass through gas utilization equipmenthaving an operating temperature in excess of500°F (260°C). [NFPA 54:9.1.8.1]508.12.2 Structural members passing throughgas utilization equipment having an operatingtemperature of 500°F (260°C) or less shall be ofnoncombustible material. Building columns,girders, beams, or trusses shall not be installedwithin equipment, unless insulation andventilation are provided to avoid alldeterioration in strength and linear expansion ofthe building structure in either a vertical or ahorizontal direction. [NFPA 54:9.1.8.2]508.12.3 Gas utilization equipment shall befurnished either with load-distributing bases orwith a sufficient number of supports to preventdamage to either the building structure orequipment. [NFPA 54:9.1.8.3]508.12.4 At the locations selected for installationof gas utilization equipment, the dynamic and

static load-carrying capacities of the buildingstructure shall be checked to determine whetherthey are adequate to carry the additional loads.The equipment shall be supported and shall beconnected to the piping so as not to exert unduestress on the connections. [NFPA 54:9.1.8.4]

508.13 Flammable Vapors. Gas appliances shallnot be installed in areas where the open use,handling, or dispensing of flammable liquidsoccurs, unless the design, operation, or installationreduces the potential of ignition of the flammablevapors. Gas utilization equipment installed incompliance with Sections 508.14, 508.15, or 508.16shall be considered to comply with the intent of thisprovision. [NFPA 54: 9.1.9]508.14 Installation in Residential Garages.

(1) Gas utilization equipment in residentialgarages and in adjacent spaces that open tothe garage and are not part of the livingspace of a dwelling unit shall be installed sothat all burners and burner-ignition devicesare located not less than 18 inches (450 mm)above the floor unless listed as flammablevapor ignition resistant. [NFPA 54:9.1.10.1]

(2) Such equipment shall be located orprotected so it is not subject to physical damageby a moving vehicle. [NFPA 54:9.1.10.2]

(3) When appliances are installed in a separate,enclosed space having access only fromoutside of the garage, such equipment maybe installed at floor level, providing therequired combustion air is taken from theexterior of the garage. [NFPA 54: 9.1.10.3]

508.15 Installation in Commercial Garages.508.15.1 Parking Structures. Gas utilizationequipment installed in enclosed, basement, andunderground parking structures shall beinstalled in accordance with NFPA 88A, Standardfor Parking Structures. [NFPA 54:9.1.11.1]508.15.2 Repair Garages. Gas utilizationequipment installed in repair garages shall beinstalled in a detached building or room,separated from repair areas by walls or partitions,floors, or floor-ceiling assemblies that areconstructed so as to prohibit the transmission ofvapors and having a fire-resistance rating of notless than 1 hour, and that have no openings in thewall separating the repair area within 8 feet (2.5 m)of the floor. Wall penetrations shall be fire-stopped. Air for combustion purposes shall beobtained from outside the building. The heatingroom shall not be used for the storage of com-bustible materials. [NFPA 54:9.1.11.2]Exception No. 1: Overhead heaters whereinstalled not less than 8 ft (2.5 m) above thefloor shall be permitted.


59

Exception No. 2: Heating equipment forvehicle repair areas where there is nodispensing or transferring of Class I or ClassII flammable or combustible liquids orliquefied petroleum gas shall be installed inaccordance with NFPA 30A, Automotive andMarine Service Station Code.[NFPA 54: 8.1.11.2]

508.16 Installation in Aircraft Hangars. Heatersin aircraft hangars shall be installed in accordancewith NFPA 409, Standard on Aircraft Hangars .[NFPA 54: 9.1.12]508.17 Gas Equipment Physical Protection.Where it is necessary to locate gas utilizationequipment close to a passageway traveled by vehiclesor equipment, guardrails or bumper plates shall beinstalled to protect the equipment from damage.[NFPA 54: 9.1.13]508.18 Venting of Flue Gases. Gas utilizationequipment shall be vented in accordance with theprovisions of this chapter and NFPA 54, Chapter 10.[NFPA 54: 9.1.14]508.19 Extra Device or Attachment. No device orattachment shall be installed on any gas utilizationequipment that could in any way impair thecombustion of gas. [NFPA 54: 9.1.15]508.20 Adequate Capacity of Piping. Whenadditional gas utilization equipment is beingconnected to a gas piping system, the existingpiping shall be checked to determine if it hasadequate capacity. (See Section 1209.4.3.) Whereinadequate, the existing system shall be enlarged asnecessary, or separate gas piping of adequatecapacity shall be run from the point of delivery tothe equipment. [NFPA 54: 9.1.16]508.21 Avoiding Strain on Gas Piping. Gasutilization equipment shall be supported and soconnected to the piping as not to exert undue strainon the connections. [NFPA 54: 9.1.17]508.22 Gas Appliance Pressure Regulators.Where the gas supply pressure is higher than that atwhich the gas utilization equipment is designed tooperate or varies beyond the design pressure limitsof the equipment, a gas appliance pressure regulatorshall be installed. [NFPA 54: 9.1.18]508.23 Venting of Gas Appliance PressureRegulators.Venting of gas appliance pressureregulators shall comply with the followingrequirements [NFPA 54:9.1.19]:

508.23.1 Gas appliance pressure regulatorsrequiring access to the atmosphere for successfuloperation shall be equipped with vent pipingleading outdoors or, if the regulator vent is anintegral part of the equipment, into thecombustion chamber adjacent to a continuous

pilot, unless constructed or equipped with a ventlimiting means to limit the escape of gas from thevent opening in the event of diaphragm failure.[NFPA 54:9.1.19(1)]508.23.2 Vent limiting means shall be employedon listed gas appliance pressure regulators only.[NFPA 54:9.1.19(2)]508.23.3 In the case of vents leading outdoors,means shall be employed to prevent water fromentering this piping and also to prevent blockageof vents by insects and foreign matter.[NFPA 54:9.1.19(3)]508.23.4 Under no circumstances shall aregulator be vented to the gas utilization equip-ment flue or exhaust system. [NFPA 54:9.1.19(4)]508.23.5 In the case of vents entering thecombustion chamber, the vent shall be located sothe escaping gas will be readily ignited by thepilot and the heat liberated thereby will notadversely affect the normal operation of thesafety shutoff system. The terminus of the ventshall be securely held in a fixed position relative tothe pilot. Formanufactured gas, the need for a flamearrester in the vent piping shall be determined.[NFPA 54:9.1.19(5)]508.23.6 Vent lines from a gas appliancepressure regulator and bleed lines from adiaphragm-type valve shall not be connected to acommon manifold terminating in a combustionchamber. Vent lines shall not terminate inpositive-pressure-type combustion chambers.[NFPA 54:9.1.19(6)]

508.24 Bleed Lines for Diaphragm-Type Valves.Bleed lines shall comply with the followingrequirements [NFPA 54:9.1.20]:

508.24.1 Diaphragm-type valves shall beequipped to convey bleed gas to the outsideatmosphere or into the combustion chamberadjacent to a continuous pilot. [NFPA 54:9.1.20(1)]508.24.2 In the case of bleed lines leadingoutdoors, means shall be employed to preventwater from entering this piping and also to preventblockage of vents by insects and foreignmatter.[NFPA 54:9.1.20(2)]508.24.3 Bleed lines shall not terminate in thegas utilization equipment flue or exhaustsystem. [NFPA 54:9.1.20(3)]508.24.4 In the case of bleed lines entering thecombustion chamber, the bleed line shall belocated so the bleed gas will be readily ignited bythe pilot and the heat liberated thereby will notadversely affect the normal operation of thesafety shutoff system. The terminus of the bleedline shall be securely held in a fixed position


60

508.15 – 508.24

relative to the pilot. For manufactured gas, theneed for a flame arrester in the bleed line pipingshall be determined. [NFPA 54:9.1.20(4)]508.24.5 Bleed lines from a diaphragm-typevalve and vent lines from a gas appliancepressure regulator shall not be connected to acommon manifold terminating in a combustionchamber. Bleed lines shall not terminate inpositive-pressure-type combustion chambers.[NFPA 54:9.1.20(5)]

508.25 Combination of Equipment. Any com-bination of gas utilization equipment, attachments,or devices used together in any manner shall complywith the standards that apply to the individualequipment. [NFPA 54: 9.1.21]508.26 Installation Instructions. The installingagency shall conform with the equipmentmanufacturer's recommendations in completing aninstallation. The installing agency shall leave themanufacturer's installation, operating, andmaintenance instructions in a location on thepremises where they will be readily available forreference and guidance for the Authority HavingJurisdiction, service personnel, and the owner oroperator. [NFPA 54: 9.1.22]508.27 Protection of Outdoor Equipment. Gasutilization equipment not listed for outdoorinstallation but installed outdoors shall be providedwith protection to the degree that the environmentrequires. Equipment listed for outdoor installationshall be permitted to be installed without protectionin accordance with the provisions of its listing. (See9.2.1.) [NFPA 54: 9.1.23]

(The following references were extracted fromNFPA 54.)9.2 Accessibility and Clearance.9.2.1 Accessibility for Service. All gas utilizationequipment shall be located with respect to buildingconstruction and other equipment so as to permitaccess to the gas utilization equipment. Sufficientclearance shall be maintained to permit clean-ing of heating surfaces; the replacement of filters,blowers, motors, burners, controls, and ventconnections; the lubrication of moving parts wherenecessary; the adjustment and cleaning of burnersand pilots; and the proper functioning of explosionvents, if provided. For attic installation, the passage-way and servicing area adjacent to the equipmentshall be floored.

509.0 Equipment on Roofs.509.1 General.

(1) Gas-utilization equipment on roofs shall bedesigned or enclosed so as to withstandclimactic conditions in the area in which theyare installed. Where enclosures are provided,

each enclosure shall permit easy entry andmovement, shall be of reasonable height, andshall have at least a 30-inches (760mm)clearance between the entire service accesspanel(s) of the equipment and the wall ofthe enclosure. [NFPA 54:9.4.1.1]

(2) Roofs on which equipment is to be installedshall be capable of supporting the additionalload or shall be reinforced to support theadditional load. [NFPA 54:9.4.1.2]

(3) All access locks, screws, and bolts shall be ofcorrosion-resistant material. [NFPA 54:9.4.1.3]

509.2 Installation of Equipment on Roofs.(1) Gas utilization equipment shall be installed in

accordance with its listing and themanufacturer's installation instructions.[NFPA 54:9.4.2.1]

(2) Equipment shall be installed on a well-drained surface of the roof. At least 6 feet(1.8m) of clearance shall be availablebetween any part of the equipment and theedge of a roof or similar hazard, or rigidlyfixed rails, guards, parapets, or otherbuilding structures at least 42 inches (1.1 m)in height shall be provided on the exposedside. [NFPA 54:9.4.2.2]

(3) All equipment requiring an external source ofelectrical power for its operation shall beprovided with (1) a readily accessibleelectrical disconnecting means within sightof the equipment that will completelyde-energize the equipment, and (2) a 120-Vac grounding-type receptacle outlet on theroof adjacent to the equipment. Thereceptacle outlet shall be on the supply sideof the disconnect switch. [NFPA 54:9.4.2.3]

(4) Where water stands on the roof at theequipment or in the passageways to theequipment, or where the roof is of a designhaving a water seal, a suitable platform,walkway, or both shall be provided above thewaterline. Such platforms or walkways shallbe located adjacent to the equipment andcontrol panels so that the equipment canbe safely serviced where water stands on theroof. [NFPA 54: 9.4.2.4]

509.3 Access to Equipment on Roofs.509.3.1 Gas utilization equipment located onroofs or other elevated locations shall be accessible.[NFPA 54:9.4.3.1]509.3.2 Buildings more than 15 feet (4.6 m) inheight shall have an inside means of access to theroof,unless other means acceptable to the AuthorityHaving Jurisdiction are used. [NFPA 54:9.4.3.2]509.3.3 The inside means of access shall be a


61

permanent, or fold-away inside stairway orladder, terminating in an enclosure, scuttle, ortrap door. Such scuttles or trap doors shall be atleast 22 inches x 24 inches (560 mm x 610 mm) insize, shall open easily and safely under allconditions, especially snow; and shall beconstructed so as to permit access from the roofside unless deliberately locked on the inside.

At least 6 feet (1.8 m) of clearance shall be avail-able between the access opening and the edge ofthe roof or similar hazard, or rigidly fixed railsor guards a minimum of 42 inches (1.1 m) in heightshall be provided on the exposed side. Whereparapets or other building structures are utilized inlieu of guards or rails, they shall be a minimumof 42 inches (1.1 m) in height. [NFPA 54:9.4.3.3]509.3.4 Permanent lighting shall be provided atthe roof access. The switch for such lightingshall be located inside the building near theaccess means leading to the roof. [NFPA 54: 9.4.3.4]

509.4 Appliances in Attics.509.4.1 Attic Access. An attic in which anappliance is installed shall be accessible throughan opening and passageway at least as large asthe largest component of the appliance, and notless than 22 inches x 30 inches (560 mm x 760 mm).[NFPA 54:9.5.1]509.4.2 Where the height of the passageway isless than 6 feet (1.8 m), the distance from thepassageway access to the appliance shall notexceed 20 feet (6.1 m) measured along thecenterline of the passageway. [NFPA 54:9.5.1.1]509.4.3 The passageway shall be unobstructedand shall have solid flooring not less than 24inches (610 mm) wide from the entrance openingto the appliance. [NFPA 54:9.5.1.2]509.4.4 Work Platform. A level workingplatform not less than 30 inches (760 mm) by 30inches (760 mm) shall be provided in front of theservice side of the appliance. [NFPA 54:9.5.2]509.4.5 Lighting and Convenience Outlet. Apermanent 120-volt receptacle outlet and alighting fixture shall be installed near theappliance. The switch controlling the lightingfixture shall be located at the entrance to thepassageway. [NFPA 54:9.5.3]

510.0 Venting of Equipment.510.1 General. This section recognizes that thechoice of venting materials and the methods ofinstallation of venting systems are dependent on theoperating characteristics of the gas utilizationequipment. The operating characteristics of vented

gas utilization equipment can be categorized withrespect to (1) positive or negative pressure within theventing system, and (2) whether or not theequipment generates flue or vent gases that cancondense in the venting system. See NFPA 54 Section3.3 for the definition of these vented appliancecategories. [NFPA 54:12.2]510.2 Specification for Venting.

510.2.1 Connection to Venting Systems.Except as permitted in Sections 510.2.2 through510.2.6, all gas utilization equipment shall beconnected to venting systems. [NFPA 54:12.3.1]510.2.2 Equipment Not Required to BeVented. The following equipment shall not berequired to be vented [NFPA 54:12.3.2]:

510.2.2.1 Listed Ranges. [NFPA 54:12.3.2(1)]510.2.2.2 Built-in Domestic Cooking UnitsListed and Marked for Optional Venting.[NFPA 54:12.3.2(2)]510.2.2.3 Listed Hot Plates and ListedLaundry Stoves. [NFPA 54:12.3.2(3)]510.2.2.4 Listed Type 1 clothes dryers shallbe exhausted to the outside air.[NFPA 54:12.3.2(4)]510.2.2.5 A single listed booster-type(automatic instantaneous) water heater,when designed and used solely for thesanitizing rinse requirements of a dish-washing machine, provided that the equip-ment is installed with the draft hood in placeand unaltered if a draft hood is required, ina commercial kitchen having a mechanicalexhaust system; where installed in thismanner, the draft hood outlet shall not beless than 36 inches (910 mm) vertically and 6inches (150mm) horizontally from any surfaceother than the equipment. [NFPA 54:12.3.2(5)]510.2.2.6 Listed Refrigerators.[NFPA 54:12.3.2(6)]510.2.2.7 Counter Appliances.[NFPA 54:12.3.2(7)]510.2.2.8 Direct Gas-Fired Makeup AirHeaters. [NFPA 54:12.3.2(9)]510.2.2.9 Other Equipment Listed forUnvented Use and Not Provided with FlueCollars. [NFPA 54:12.3.2(10)]510.2.2.10 Specialized Equipment ofLimited Input such as Laboratory Burners orGas Lights. [NFPA 54:12.3.2(11)] Where anyor all of this equipment in Sections 510.2.2.1through 510.2.2.10 is installed so theaggregate input rating exceeds 20 Btu/h/ft3


62

509.3 – 510.2

(207 W/m3) of room or space in which it isinstalled, one or more shall be provided withventing systems or other approved means forremoving the vent gases to the outsideatmosphere so the aggregate input rating ofthe remaining unvented equipment does notexceed 20 Btu/h/ft3 (207 W/m3). Where thecalculation includes the volume of an adjacentroom or space, the room or space in which theequipment is installed shall be directlyconnected to the adjacent room or space by adoorway, archway, or other opening ofcomparable size that cannot be closed.

510.2.3 Ventilating Hoods. Ventilating hoodsand exhaust systems shall be permitted to beused to vent gas utilization equipment installed incommercial applications (see Section 510.3.5)and to vent industrial equipment, particularlywhere the process itself requires fume disposal.[NFPA 54:12.3.3]510.2.4 Well-Ventilated Spaces. The operation ofindustrial gas utilization equipment such that itsflue gases are discharged directly into a large andwell-ventilated space shall be permitted. [NFPA54:12.3.4]510.2.5 Direct-Vent Equipment. Listed direct-vent gas utilization equipment shall beconsidered properly vented where installed inaccordance with the terms of its listing, themanufacturer's instructions, and Section 510.8(3)of this code. [NFPA 54:12.3.5]510.2.6 Equipment with Integral Vents. Gasutilization equipment incorporating integralventing means shall be considered properlyvented where installed in accordance with itslisting, the manufacturer's instructions, andSections 510.8.1 and 510.8.2 of this code. [NFPA54:12.3.6]

510.3 Design and Construction.510.3.1 Minimum Safe Performance. A ventingsystem shall be designed and constructed so as todevelop a positive flow adequate to remove flue orvent gases to the outside atmosphere.510.3.2 Equipment Draft Requirements. Aventing system shall satisfy the draft require-ments of the equipment in accordance with themanufacturer's instructions. [NFPA 54:12.4.1]510.3.3 Design and Construction. Gasutilization equipment required to be vented shallbe connected to a venting system designed andinstalled in accordance with the provisions ofSections 510.4 through 510.15 of this code.[NFPA 54:12.4.2]

510.3.4 Mechanical Draft Systems.510.3.4.1 Mechanical draft systems shall belisted and shall be installed in accordancewith the terms of their listing and both theappliance and the mechanical draft systemmanufacturers' instructions. [NFPA54:12.4.3.1]510.3.4.2 Gas utilization equipmentrequiring venting shall be permitted to bevented by means of mechanical draftsystems of either forced or induced draftdesign. [NFPA 54:12.4.3.2]Exception: Incinerators.

510.3.4.3 Forced draft systems and allportions of induced draft systems underpositive pressure during operation shall bedesigned and installed so as to preventleakage of flue or vent gases into a building.[NFPA 54:12.4.3.3]510.3.4.4 Vent connectors serving equipmentvented by natural draft shall not be connectedinto any portion of mechanical draft systemsoperating under positive pressure.[NFPA 54:12.4.3.4]510.3.4.5 Where a mechanical draft systemis employed, provision shall be made toprevent the flow of gas to the main burnerswhen the draft system is not performing so asto satisfy the operating requirements of theequipment for safe performance.[NFPA54:12.4.3.4]510.3.4.6 The exit terminals of mechanicaldraft systems shall be not less than 7 feet (2.1m)above grade where located adjacent to publicwalkways and shall be located as specified inSections 510.8.1 and 510.8.2 of this code.[NFPA54:12.4.3.6]

510.3.5 Ventilating Hoods and ExhaustSystems.

510.3.5.1 Ventilating hoods and exhaustsystems shall be permitted to be used to ventgas utilization equipment installed incommercial applications. [NFPA54:12.4.4.1]510.3.5.2 Where automatically operated gasutilization equipment is vented through aventilating hood or exhaust system equippedwith a damper or with a power means ofexhaust, provisions shall be made to allowthe flow of gas to the main burners onlywhen the damper is open to a position toproperly vent the equipment and when thepower means of exhaust is in operation.[NFPA54:12.4.4.2]

510.3.6 Circulating Air Ducts and FurnacePlenums. No portion of a venting system shall


63

extend into or pass through any circulating airduct or furnace plenum. [NFPA 54:12.4.5.1]

510.4 Type of Venting System to Be Used.510.4.1 The type of venting system to be used shallbe in accordancewithTable 5-2. [NFPA54:12.5.1]510.4.2 Plastic Piping. Plastic piping used forventing equipment listed for use with suchventingmaterials shall be approved. [NFPA54:12.5.2]510.4.3 Special Gas Vent. Special gas vent shallbe listed and installed in accordance with theterms of the special gas vent listing and themanufacturer's instructions. [NFPA 54:12.5.3]

510.5 Masonry, Metal, and Factory-BuiltChimneys.

510.5.1 Listing or Construction.510.5.1.1 Factory-built chimneys shall beinstalled in accordance with their listing andthe manufacturers' instructions. Factory-builtchimneys used to vent appliances thatoperate at positive vent pressure shall belisted for such application. [NFPA54:12.6.1.1]510.5.1.2 Metal chimneys shall be built andinstalled in accordance with NFPA 211,Standard for Chimneys, Fireplaces, Vents, andSolid Fuel-Burning Appliances. [NFPA54:12.6.1.2]510.5.1.3 Masonry chimneys shall be builtand installed in accordance with NFPA 211,Standard for Chimneys, Fireplaces, Vents, andSolid Fuel-Burning Appliances, and lined withapproved clay flue lining, a listed chimneylining system, or other approved materialthat will resist corrosion, erosion, softening,or cracking from vent gases at temperaturesup to 1800°F (982°C). [NFPA54:12.6.1.3]Exception: Masonry chimney flues linedwith a chimney lining system specificallylisted for use with listed gas applianceswith draft hoods, Category I appliances,and other gas appliances listed for usewith Type B vents shall be permitted.The liner shall be installed in accordancewith the liner manufacturer's instructionsand the terms of the listing. A permanentidentifying label shall be attached at thepoint where the connection is to bemade to the liner. The label shall read:"This chimney liner is for appliances thatburn gas only. Do not connect to solid-orliquid-fuel-burning appliances orincinerators." [NFPA54:12.6.1.3]

510.5.2 Termination.510.5.2.1 A chimney for residential-type orlow-heat gas utilization equipment shall

extend at least 3 feet (0.9 m) above thehighest point where it passes through a roofof a building and at least 2 feet (0.6 m)higher than any portion of a building withina horizontal distance of 10 feet (3.0 m). [SeeFigure 5-1.] [NFPA 54:12.6.2.1]510.5.2.2 A chimney for medium-heatequipment shall extend at least 10 feet (3.0 m)higher than any portion of any buildingwithin 25 feet (7.6 m). [NFPA 54:12.6.2.2]510.5.2.3 A chimney shall extend at least 5 feet(1.5 m) above the highest connected equip-ment draft hood outlet or flue collar.[NFPA 54:12.6.2.3]510.5.2.4 Decorative shrouds shall not beinstalled at the termination of factory-builtchimneys except where such shrouds arelisted and labeled for use with the specificfactory-built chimney system and areinstalled in accordance with manufacturers'installation instructions. [NFPA 54:12.6.2.4]

510.5.3 Size of Chimneys. The effective area ofa chimney venting system serving listed gasappliances with draft hoods, Category Iappliances, and other appliances listed for usewith Type B vents shall be in accordance withone of the following methods [NFPA54:12.6.3.1(1)]:(1) This chapter and NFPA 54: Chapter 13.

[NFPA 54:12.6.3.1(1)](2) For sizing an individual chimney venting

system for a single appliance with a drafthood, the effective areas of the ventconnector and chimney flue shall be not lessthan the area of the appliance flue collar ordraft hood outlet or greater than seven timesthe draft hood outlet area. [NFPA 54:12.6.3.1(2)]

(3) For sizing a chimney venting system connectedto two appliances with draft hoods, theeffective area of the chimney flue shall benot less than the area of the larger draft hoodoutlet plus 50 percent of the area of thesmaller draft hood outlet, or greater thanseven times the smallest draft hood outlet area.[NFPA 54:12.6.3.1(3)]

(4) Other approved engineering methods.[NFPA 54:12.6.3.1(5)]

(5) Chimney venting systems using mechanicaldraft shall be sized in accordance with approvedengineering methods. [NFPA 54:12.6.3.1(4)]Where an incinerator is vented by a chimneyserving other gas utilization equipment, thegas input to the incinerator shall not beincluded in calculating chimney size, providedthe chimney flue diameter is not less than 1


64

510.3 – 510.5

inch (25 mm) larger in equivalent diameterthan the diameter of the incinerator flueoutlet. [NFPA 54:12.6.3.2]

510.5.4 Inspection of Chimneys.(A) Before replacing an existing appliance or

connecting a vent connector to a chimney,the chimney passageway shall be examinedto ascertain that it is clear and free ofobstructions and shall be cleaned ifpreviously used for venting solid- or liquid-fuel-burning appliances or fireplaces.[NFPA 54:12.6.4.1]

(B) Chimneys shall be lined in accordance withNFPA 211, Standard for Chimneys, Fireplaces,Vents, and Solid-Fuel Burning Appliances.[NFPA 54:12.6.4.2]

(C) Cleanouts shall be examined to determinethat they will remain tightly closed whennot in use. [NFPA 54:12.6.4.3]

(D) When inspection reveals that an existingchimney is not safe for the intendedapplication, it shall be repaired, rebuilt,lined, relined, or replaced with a vent orchimney to conform to NFPA 211, Standardfor Chimneys, Fireplaces, Vents, and Solid-Fuel-Burning Appliances, and shall besuitable for the equipment to be attached.[NFPA 54:12.6.4.4]

510.5.5 Chimney Serving Equipment BurningOther Fuels.

510.5.5.1 Gas utilization equipment shallnot be connected to a chimney flue serving aseparate appliance designed to burn solidfuel. [NFPA 54:12.6.5.1]510.5.5.2 Where one chimney serves gasutilization equipment and equipmentburning liquid fuel, the equipment shall beconnected through separate openings orshall be connected through a single openingwhere joined by a suitable fitting located asclose as practical to the chimney. Where twoor more openings are provided into onechimney flue, they shall be at differentlevels. Where the gas utilization equipmentis automatically controlled, it shall beequipped with a safety shutoff device.[NFPA 54:12.6.5.2]510.5.5.3 A listed combination gas- andsolid-fuel-burning appliance connected to asingle chimney flue shall be equipped with amanual reset device to shut off gas to themain burner in the event of sustainedbackdraft or flue gas spillage. The chimneyflue shall be sized to properly vent theappliance. [NFPA 54: 12.6.5.3]

WATER HEATERS Figure 5-1 – 510.5

65

FIGURE 5-1 Typical Termination Locations forChimneys and Single-Wall Metal Pipes ServingResidential-Type and Low-Heat Equipment[NFPA 54:Figure 12.6.2.1]

TABLE 5-2Type of Venting System to Be Used

Gas Utilization Equipment Type of Venting System

Listed Category I equipment Type B gas vent (510.6)Listed equipment equipped Chimney (510.5)

with draft hood Single-wall metal pipeEquipment listed for use with (510.7)

Type B gas vent Listed chimney liningsystem for gas venting (510.5.1.3)

Special gas vent listedfor this equipment(510.4.3)

Listed vented wall furnaces Type B-W gas vent(510.6, 510.6.2.2)

Category II equipment As specified orfurnished

Category III equipment By manufacturers oflisted

Category IV equipment equipment (510.4.2,510.4.3)

Incinerators, outdoors Single-wall metal pipe(510.7, 510.7.3)

Incinerators, indoors Chimney (510.5)Equipment that can be converted

to use of solid fuelUnlisted combination gas- and

oil-burning equipmentCombination gas- and solid-fuel-

burning equipmentEquipment listed for use with

chimneys onlyUnlisted equipment

Listed combination gas- and Type L vent (510.6) oroil-burning equipment chimney (510.5)

Decorative appliance in vented Chimney [UMC 907.2(3)]fireplace

Gas-fired toilets Single-wall metal pipe(510.7, NFPA 54: 9.25.3)

Direct-vent equipment See 510.2.5

Equipment with integral vent See 510.2.6

[NFPA 54: Table 12.5.1]

510.5.5.4 A single chimney flue serving alisted combination gas- and oil-burningappliance shall be sized to properly vent theappliance. [NFPA 54: 12.6.5.4]

510.5.6 Support of Chimneys. All portions ofchimneys shall be supported for the design andweight of the materials employed. Listedfactory-built chimneys shall be supported andspaced in accordance with their listings and themanufacturers' instructions. [NFPA 54: 12.6.6]


66

Figure 5-2 – 510.5

FIGURE 5-3 Plan View of Practical SeparationMethod for Multistory Gas Venting. [NFPA 54:Figure 12.7.4.2]

Roof pitch heights

Roof pitch H(minimum) ft. mFlat to 6/12 1.0 0.30Over 6/12 to 7/12 1.25 0.38Over 7/12 to 8/12 1.5 0.46Over 8/12 to 9/12 2.0 0.61Over 9/12 to 10/12 2.5 0.76Over 10/12 to 11/12 3.25 0.99Over 11/12 to 12/12 4.0 1.22Over 12/12 to 14/12 5.0 1.52Over 14/12 to 16/12 6.0 1.83Over 16/12 to 18/12 7.0 2.13Over 18/12 to 20/12 7.5 2.27Over 20/12 to 21/12 8.0 2.44

FIGURE 5-2 Gas Vent Termination Locations forListed Caps 12 in. (300 mm) or Less in Size atLeast 8 ft. (2.4 m) from a Vertical Wall [NFPA 54:Figure 12.7.2 and Table 12.7.2]

510.5.7 Cleanouts. Where a chimney thatformerly carried flue products from liquid- orsolid-fuel-burning appliances is used with anappliance using fuel gas, an accessible cleanoutshall be provided. The cleanout shall have atight-fitting cover and be installed so its upperedge is at least 6 inches (150 mm) below thelower edge of the lowest chimney inlet opening.[NFPA 54: 12.6.7]510.5.8 Space Surrounding Lining or Vent.

510.5.8.1 The remaining space surrounding achimney liner, gas vent, special gas vent, orplastic piping installed within a masonrychimney flue shall not be used to vent anotherappliance. [NFPA 54: 12.6.8.1]Exception: The insertion of another lineror vent within the chimney as providedin this code and the liner or ventmanufacturer's instructions.

510.5.8.2 The remaining space surroundinga chimney liner, gas vent, special gas vent,or plastic piping installed within a masonrychimney flue shall not be used to supplycombustion air. [NFPA 54: 12.6.8.2]Exception: Direct-vent gas-firedappliances designed for installation in asolid-fuel-burning fireplace whereinstalled in accordance with the listingand the manufacturer’s instruction.

510.6 Gas Vents.510.6.1 A gas vent passing through a roof shallextend through the entire roof flashing, roof jack,or roof thimble and be terminated with a listedtermination cap. [NFPA 54-2002: 10.6.1(3)]

510.6.1.1 Type B or Type L vents shallextend in a generally vertical direction withoffsets not exceeding 45 degrees, except thata vent system having not more than one60-degree offset shall be permitted. Anyangle greater than 45 degrees from thevertical is considered horizontal. The totalhorizontal distance of a vent plus thehorizontal vent connector serving draft-hood-equipped appliances shall not begreater than 75 percent of the vertical heightof the vent. [NFPA 54-2002: 10.6.1(4)]Exception: Systems designed and sizedas provided in this chapter or in accor-dance with other approved engineeringmethods.

510.6.1.2 Vents serving Category I fan-assisted appliances shall be installed inaccordance with the appliance manufacturer'sinstructions and NFPA 54, Chapter 10 orother approved engineering methods.[NFPA 54: 12.7.1(3)]

510.6.2 A gas vent shall terminate in accordancewith one of the following [NFPA 54: 12.7.2(1)]:(1) Above the roof surface with a listed cap

or listed roof assembly. Gas vents 12 inches(300 mm) in size or smaller with listedcaps shall be permitted to be terminated inaccordance with Figure 5-2, provided theyare at least 8 feet (2.4 m) from a vertical wallor similar obstruction. All other gas ventsshall terminate not less than 2 feet (0.6 m)above the highest point where they passthrough the roof and at least 2 feet (0.6 m)higher than any portion of a building within10 feet (3.1 m).

(2) Industrial gas utilization equipment asprovided inSection510.2.4. [NFPA54:12.7.2(1)(c)]

(3) Direct-vent systems as provided in Section510.2.5. [NFPA 54: 12.7.2(1)(d)]

(4) Equipment with integral vents as providedin Section 510.2.6. [NFPA 54: 12.7.2(1)(e)]

(5) Mechanical draft systems as provided inSection 510.3.4. [NFPA 54: 12.7.2(1)(f)]

(6) Ventilating hoods and exhaust systemsas provided in Section 510.3.5. [NFPA 54:12.7.2(1)(g)]510.6.2.1 A Type B or a Type L gas ventshall terminate at least 5 feet (1.5 m) invertical height above the highest connectedequipment draft hood or flue collar. [NFPA54: 12.7.2(2)]510.6.2.2A Type B-W gas vent shall terminateat least 12 feet (3.7 m) in vertical heightabove the bottom of the wall furnace. [NFPA54: 12.7.2(3)]510.6.2.3 A gas vent extending through anexterior wall shall not terminate adjacent tothe wall or below eaves or parapets, exceptas provided in Sections 510.2.5 and 510.3.4.[NFPA 54: 12.7.2(4)]510.6.2.4 Decorative shrouds shall not beinstalled at the termination of gas ventsexcept where such shrouds are listed for usewith the specific gas venting system and areinstalled in accordance with manufacturers'installation instructions. [NFPA 54: 12.7.2(5)]510.6.2.5 All gas vents shall extend throughthe roof flashing, roof jack, or roof thimbleand terminate with a listed cap or listed roofassembly. [NFPA 54:12.7.2(6)]510.6.2.6 A gas vent shall terminate at least3 feet (0.9m) above a forced air inlet locatedwithin 10 feet (3.0m). [NFPA 54:12.7.2(7)]

510.6.3 Size of Gas Vents. Venting systems

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510.5 – 510.6


68

shall be sized and constructed in accordancewith NFPA 54, Chapter 3 or other approvedengineering methods and the gas vent and gasequipment manufacturers' instructions. [NFPA54: 12.7.3]

510.6.3.1 Category I Appliances. Thesizing of natural draft venting systemsserving one or more listed appliancesequipped with a draft hood or applianceslisted for use with Type B gas vent, installedin a single story of a building, shall be inaccordance with one of the followingmethods. [NFPA 54: 12.7.3.1](1) The provisions of this chapter. [NFPA

54: 12.7.3.1(1)](2) Vents serving fan-assisted combustion

system appliances, or combinations offan-assisted combustion systems anddraft hood-equipped appliances, shallbe sized in accordance with this chapteror other approved engineering methods.[NFPA 54: 12.7.3.1(2)]

(3) For sizing an individual gas vent for asingle, draft-hood-equipped appliance,the effective area of the vent connectorand the gas vent shall be not less thanthe area of the appliance draft hoodoutlet or greater than seven times thedraft hoodoutlet area. [NFPA54: 12.7.3.1(3)]

(4) For sizing a gas vent connected to twoappliances with draft hoods, the effectivearea of the vent shall be not less than thearea of the larger draft hood outlet plus50 percent of the area of the smaller drafthood outlet or greater than seven timesthe smaller draft hood outlet area.[NFPA 54: 12.7.3.1(4)]

(5) Approved engineering practices. [NFPA54: 12.7.3.1(5)]

510.6.3.2 Category II, Category III, andCategory IV Appliances. The sizing of gasvents for Category II, Category III, andCategory IV gas utilization equipment shallbe in accordance with the equipment

510.6 – Table 5-3

TABLE 5-3Clearance for Connectors [NFPA 54: Table 12.8.4.4]

Minimum Distance from Combustible Material

Listed Type B Listed Type L Single-Wall Factory-BuiltEquipment Gas Vent Material Vent Material Metal Pipe Chimney SectionsListed equipment with As listed As listed 6 in. As listeddraft hoods and equip-ment listed for use withType B gas vents

Residential boilers and 6 in. 6 in. 9 in. As listedfurnaces with listed gasconversion burner andwith draft hood

Residential appliances Not permitted As listed 9 in. As listedlisted for use with Type Lvents

Residential incinerators Not permitted 9 in. 18 in. As listed

Listed gas-fired toilets Not permitted As listed As listed As listed

Unlisted residential Not permittted 6 in. 9 in. As listedappliances with drafthood

Residential and low-heat Not permitted 9 in. 18 in. As listedequipment other thanthose above

Medium-heat equipment Not permitted Not permitted 36 in. As listed

For SI units, 1 in.= 25.4 mm.Note: These clearances shall apply unless the listing of an appliance or connector specifies clearances, in which case the listed clearancesshall apply.

manufacturers' instructions. [NFPA54:12.7.3.3]510.6.3.3 Sizing. Chimney venting systemsusing mechanical draft shall be sized inaccordance with approved engineeringmethods. [NFPA 54:12.7.3.4]

510.6.4 Gas Vents Serving Equipment onMore Than One Floor.

510.6.4.1 A common gas vent shall bepermitted in multistory installations to ventCategory I gas utilization equipment locatedon more than one floor level, provided theventing system is designed and installed inaccordance with approved engineeringmethods.For the purpose of this section, crawl spaces,basements, and attics shall be considered asfloor levels. [NFPA 54: 12.7.4.1]510.6.4.2 All gas utilization equipmentconnected to the common vent shall belocated in rooms separated from a habitablespace. Each of these rooms shall haveprovisions for an adequate supply ofcombustion, ventilation, and dilution airthat is not supplied from a habitable space.(See Figure 5-3.) [NFPA 54: 12.7.4.2]

The size of the connectors andcommon segments of multistory ventingsystems for gas utilization equipment listedfor use with Type B double-wall gas ventshall be in accordance with Table 5-14,provided [NFPA 54: 12.7.4.3]:(1) The available total height (H) for eachsegment of a multistory venting system isthe vertical distance between the level ofthe highest draft hood outlet or flue collaron that floor and the centerline of the nexthighest interconnection tee. (See FigureG.1(K).) [NFPA 54: 12.7.4.2(1)]

(2) The size of the connector for a segment isdetermined from its gas utilization equipmentheat input and available connector rise, andshall not be smaller than the draft hood outletor flue collar size. [NFPA 54: 12.7.4.2(2)]

(3) The size of the common vertical ventsegment, and of the interconnection tee atthe base of that segment, shall be based onthe total gas utilization equipment heatinput entering that segment and its availabletotal height. [NFPA 54: 12.7.4.2(3)]

510.6.5 Support of Gas Vents. Gas vents shallbe supported and spaced in accordance withtheir listings and the manufacturers' instructions.[NFPA 54: 12.7.5]510.6.6 Marking. In those localities where solid

and liquid fuels are used extensively, gas ventsshall be permanently identified by a labelattached to the wall or ceiling at a point wherethe vent connector enters the gas vent. The labelshall read: "This gas vent is for appliances thatburn gas. Do not connect to solid- or liquid-fuel-burning appliances or incinerators." TheAuthority Having Jurisdiction shall determinewhether its area constitutes such a locality.[NFPA 54:12.7.6]

510.7 Single-Wall Metal Pipe.510.7.1 Construction. Single-wall metal pipeshall be constructed of galvanized sheet steel notless than 0.0304 inch (0.7 mm) thick or of otherapproved, noncombustible, corrosion-resistantmaterial. [NFPA 54: 12.8.1]510.7.2 Cold Climate. Uninsulated single-wallmetal pipe shall not be used outdoors in coldclimates for venting gas utilization equipmentin regions where the 99 percent winter designtemperature is below 32˚ Fahrenheit.[NFPA 54:12.8.2]510.7.3 Termination. The termination of single-wall metal pipe shall comply with the followingrequirements [NFPA 54: 12.8.3]:

510.7.3.1 Single-wall metal pipe shallterminate at least 5 feet (1.5 m) in verticalheight above the highest connected equip-ment draft hood outlet or flue collar.[NFPA 54: 12.8.3(1)]510.7.3.2 Single-wall metal pipe shallextend at least 2 feet (0.6 m) above the highestpoint where it passes through the roof of abuilding and at least 2 feet (0.6 m) higher thanany portion of a building within a horizontaldistance of 10 feet (3.1 m). [See Figure 5-1.][NFPA 54: 12.8.3(2)]510.7.3.3 An approved cap or roof assemblyshall be attached to the terminus of a single-wall metal pipe. [Also see Section 510.7.4.2.][NFPA 54: 12.8.3(3)]

510.7.4 Installation with Equipment Permittedby 510.4.1.

510.7.4.1 Single-wall metal pipe shall beused only for runs directly from the spacein which the gas utilization equipment islocated through the roof or exterior wall tothe outer air. A pipe passing through aroof shall extend without interruptionthrough the roof flashing, roof jacket, orroof thimble. [NFPA 54: 12.8.4.1]510.7.4.2 Single-wall metal pipe shall notoriginate in any unoccupied attic orconcealed space and shall not pass throughany attic, inside wall, concealed space, orfloor. For the installation of a single-wall

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510.6 – 510.7

Table 5-4Reduction of Clearances with Specified Forms of Protection [NFPA 54:Table 10.2.3(b)]

Where the required clearance with no protection from appliance, vent connector, orsingle-wall metal pipe is:

36 in. 18 in. 12 in. 9 in. 6 in.Allowable Clearances with Specified Protection (in.)

Type of protection appliedto and covering all surfaces Use Col. 1 for clearances above appliance or horizontal connector. Use Col. 2 forof combustible material clearances from appliances, vertical connector, and single-wall metal pipe.within the distance specifiedas the required clearance Sides Sides Sides Sides Sideswith no protection [See and and and and andFigures 5-4 Above Rear Above Rear Above Rear Above Rear Above Rearthrough 5-6.] Col. 1 Col. 2 Col. 1 Col. 2 Col. 1 Col. 2 Col. 1 Col. 2 Col. 1 Col. 2(1) 3-1/2 in. thick masonry -- 24 -- 12 -- 9 -- 6 -- 5wall without ventilated airspace(2) 1/2 in. insulation board 24 18 12 9 9 6 6 5 4 3over 1 in. glass fiber ormineral wool batts(3) 0.024 sheet metal over 18 12 9 6 6 4 5 3 3 31 in. glass fiber or mineralwool batts reinforced withwire on rear face withventilated air space(4) 3-1/2 in. thick masonry -- 12 -- 6 -- 6 -- 6 -- 6wall with ventilated airspace(5) 0.024 sheet metal with 18 12 9 6 6 4 5 3 3 2ventilated air space(6) 1/2 in. thick insulation 18 12 9 6 6 4 5 3 3 3board with ventilated airspace(7) 0.024 sheet metal with 18 12 9 6 6 4 5 3 3 3ventilated air space over0.024 sheet metal withventilated air space(8) 1 in. glass fiber or 18 12 9 6 6 4 5 3 3 3mineral wool battssandwiched between twosheets 0.024 sheet metalwith ventilated air space

For SI units, 1 in. = 25.4 mm.Notes:1. Reduction of clearances from combustible materials shall not interfere with combustion air, draft hood clearance and relief, andaccessibility of servicing.2. All clearances shall be measured from the outer surface of the combustible material to the nearest point on the surface of the appliance,disregarding any intervening protection applied to the combustible material.3. Spacers and ties shall be of noncombustible material. No spacer or tie shall be used directly opposite the appliance or connector.4. Where all clearance reduction systems use a ventilated air space, adequate provision for air circulation shall be provided as described.[See Figure 5-5 and Figure 5-6.]5. There shall be at least 1 in. (25 mm) between clearance reduction systems and combustible walls and ceilings for reduction systems usinga ventilated air space.6. Where a wall protector is mounted on a single flat wall away from corners, it shall have a minimum 1 inch (25 mm) air gap. To provideadequate air circulation, the bottom and top edges, or only the side and top edges, or all edges shall be left open.7. Mineral wool batts (blanket or board) shall have a minimum density of 8 lb/ft3 (128 kg/m3) and a minimummelting point of 1,500˚F (816˚C).8. Insulation material used as part of a clearance reduction system shall have a thermal conductivity of 1.0 Btu in./ft2 /h-˚F (0.144 W/m-K)or less.9. There shall be at least 1 inch (25 mm) between the appliance and the protector. In no case shall the clearance between the appliance andthe combustible surface be reduced below that allowed in this table.10. All clearances and thicknesses are minimum; larger clearances and thicknesses are acceptable.11. Listed single-wall connectors shall be installed in accordance with the terms of their listing and the manufacturers’ instructions.


70

Table 5-4

metal pipe through an exterior combustiblewall, see Section 510.10.14.2. [NFPA 54:12.8.4.2]510.7.4.3 Single-wall metal pipe used forventing an incinerator shall be exposed andreadily examinable for its full length andshall have suitable clearances maintained.[NFPA 54:12.8.4.3]510.7.4.4 Minimum clearances from single-wall metal pipe to combustible material shallbe in accordance with Table 5-3. Reducedclearances from single-wall metal pipe tocombustible material shall be as specified forvent connectors in Table 5-4. [NFPA 54:12.8.4.4]510.7.4.5 Where a single-wall metal pipepasses through a roof constructed ofcombustible material, a noncombustible,nonventilating thimble shall be used at thepoint of passage. The thimble shall extend at

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Figure 5-4 – 510.7

Notes:A – Equals the clearance with no protection specified inTables 5-3 and 5-4 and in the sections applying tovarious types of equipment.B – Equals the reduced clearance permitted inaccordance with Table 5-3. The protection applied to theconstruction using combustible material shall extend farenough in each direction to make C equal to A.

FIGURE 5-4 Extent of Protection Necessary toReduce Clearances from Gas Equipment or VentConnectors. [NFPA 54:Figure 10.3.2.2(a)]

Masonry walls can be attached to combustible wallsusing wall ties. Spacers should not be used directlybehind appliance or connector.FIGURE 5-5 Wall Protection Reduction System.[NFPA 54:Figure 10.3.2.2(b)]

TABLE 5-5Minimum Thickness for Galvanized Steel Vent

Connector for Low-Heat Appliances[NFPA 54:Table 12.11.2.5]

Diameter of Minimum ThicknessConnector (in.) (in.)*

Less than 6 0.0196 to less than 10 0.02310 to 12 inclusive 0.02914 to 16 inclusive 0.034

Over 16 0.056

* For SI units, 1 in. = 25.4 mm; 1 in.2 = 645 mm2.

FIGURE 5-6 Masonry Clearance Reduction System.[NFPA 54:Figure 10.3.2.2(c)]

least 18 inches (460 mm) above and 6 inches(150 mm) below the roof with the annularspace open at the bottom and closed only atthe top. The thimble shall be sized inaccordance with Section 510.10.14.2. [NFPA54: 12.8.4.5]

510.7.5 Size of Single-Wall Metal Pipe. Single-wall metal piping shall comply with thefollowing requirements [NFPA 54: 12.8.5]:

510.7.5.1 A venting system of a single-wallmetal pipe shall be sized in accordance withone of the following methods and the gasequipment manufacturer's instructions[NFPA 54: 12.8.5(1)]:

(1) For a draft-hood-equipped appliance, inaccordance with this chapter.[NFPA 54: 12.8.5(1,a)]

(2) For a venting system for a singleappliance with a draft hood, the areas ofthe connector and the pipe each shallnot be less than the area of theappliance flue collar or draft hoodoutlet, whichever is smaller. The ventarea shall not be greater than seventimes the draft hood outlet area.[NFPA 54: 12.8.5(1,b)]

(3) Other approved engineering methods.[NFPA 54: 12.8.5(1,c)]

510.7.5.2Where a single-wall metal pipe isused and has a shape other than round, itshall have an equivalent effective area equalto the effective area of the round pipe forwhich it is substituted, and the minimuminternal dimension of the pipe shall be 2inches (50 mm). [NFPA 54: 12.8.5(2)]510.7.5.3 The vent cap or a roof assemblyshall have a venting capacity not less thanthat of the pipe to which it is attached.[NFPA 54: 12.8.5(3)]

510.7.6 Support of Single-Wall Metal Pipe.All portions of single-wall metal pipe shall besupported for the design and weight of thematerial employed. [NFPA 54: 12.8.6]510.7.7 Marking. Single-wall metal pipe shallcomply with the marking provisions of Section510.6.6. [NFPA 54:12.8.7]

510.8 Through-the-Wall Vent Termination. (SeeFigure 5-12.)

510.8.1 A mechanical draft venting system shallterminate at least 3 feet (0.9 m) above any forcedair inlet located within 10 feet (3.1 m).[NFPA 54: 12.9.1]

Exception No. 1: This provision shall notapply to the combustion air intake of adirect-vent appliance.Exception No. 2: This provision shall notapply to the separation of the integraloutdoor air inlet and flue gas discharge oflisted outdoor appliances.

510.8.2 A mechanical draft venting system ofother than direct-vent type shall terminate atleast 4 feet (1.2 m) below, 4 feet (1.2 m) horizon-tally from, or 1 foot (300 mm) above anydoor,operable window, or gravity air inlet into anybuilding. The bottom of the vent terminal shallbe located at least 12 inches (300 mm) above grade.[NFPA 54: 12.9.2]510.8.3 The vent terminal of a direct-ventappliance with an input of 10,000 Btu/h (3 kW)or less shall be located at least 6 inches (150 mm)from any air opening into a building, and suchan appliance with an input over 10,000 Btu/h (3kW) but not over 50,000 Btu/h (14.7 kW) shall beinstalled with a 9-inch (230 mm) venttermination clearance, and an appliance with aninput over 50,000 Btu/h (14.7 kW) shall have atleast a 12 inch (300-mm) vent terminationclearance. The bottom of the vent terminal andthe air intake shall be located at least 12 inches (300mm) above grade. [NFPA 54: 12.9.3]510.8.4 Through-the-wall vents for Category IIand Category IV appliances and noncategorizedcondensing appliances shall not terminate overpublic walkways or over an area wherecondensate or vapor could create a nuisance orhazard or could be detrimental to the operationof regulators, relief valves, or other equipment.Where local experience indicates that condensateis a problem with Category I and Category IIIappliances, this provision shall also apply.[NFPA 54:12.9.4]

510.9 Condensation Drain.510.9.1 Provision shall be made to collect anddispose of condensate from venting systemsserving Category II and Category IV gasutilization equipment and noncategorizedcondensing appliances in accordance withSection 510.8.4. [NFPA 54: 12.10.1]510.9.2 Where local experience indicates thatcondensation is a problem, provision shall bemade to drain off and dispose of condensatefrom venting systems serving Category I andCategory III gas utilization equipment inaccordance with 510.8.4. [NFPA 54:10.9.2]

510.10 Vent Connectors for Category I GasUtilization Equipment.


72

510.7 – 510.10

510.10.1 Where Required. A vent connectorshall be used to connect gas utilizationequipment to a gas vent, chimney, or single-wall metal pipe, except where the gas vent,chimney, or single-wall metal pipe is directlyconnected to the equipment. [NFPA 54: 12.11.1]510.10.2 Materials.

510.10.2.1 A vent connector shall bemade of noncombustible, corrosion resis-tant material capable of withstandingthe vent gas temperature produced by thegas utilization equipment and of sufficientthickness to withstand physical damage.[NFPA 54: 12.11.2.1]510.10.2.2 Where the vent connector usedfor gas utilization equipment having a drafthood or a Category I appliance is located inor passes through an unconditioned area,that portion of the vent connector shall belisted Type B, Type L, or listed vent materialhaving equivalent insulation qualities.[NFPA 54: 12.11.2.2]Exception: Single-wall metal pipelocated within the exterior walls of thebuilding and located in areas having alocal 99 percent winter design temperatureof 5˚F or higher.

510.10.2.3 Where the vent connector usedfor gas utilization equipment having a drafthood or a Category I appliance is located inor passes through attics and crawl spaces,that portion of the vent connector shall belisted Type B, Type L, or listed vent materialhaving equivalent insulation qualities.[NFPA 54: 12.11.2.3]510.10.2.4 Vent connectors for residential-type appliances shall comply with thefollowing: [NFPA 54: 12.11.2.4](1) Vent Connectors Not Installed in Attics,

Crawl Spaces, or Other UnconditionedAreas. Vent connectors for listed gasappliances having draft hoods and forappliances having draft hoods andequipped with listed conversionburners that are not installed in attics,crawl spaces, or other unconditionedareas shall be one of the following:

(a) Type B or Type L vent material.(b) Galvanized sheet steel not less than

0.018-inches (0.46 mm) thick.(c) Aluminum (1100 or 3003 alloy or

equivalent) sheet not less than 0.027-inches (0.69 mm) thick.

(d) Stainless steel sheet not less than 0.012-inches (0.31 mm) thick.

(e) Smooth interior wall metal pipe havingresistance to heat and corrosion equal toor greater than that of b, c, or d above.

(f) A listed vent connector.(2) Vent connectors shall not be covered

with insulation.Exception: Listed insulated ventconnectors shall be installed according tothe terms of their listing.

510.10.2.5 A vent connector for non-residential low-heat equipment shall be afactory-built chimney section or steel pipehaving resistance to heat and corrosionequivalent to that for the appropriategalvanized pipe as specified in Table 5-5.Factory-built chimney sections shall bejoined together in accordance with thechimney manufacturer's instructions.[NFPA 54: 12.11.2.5]510.10.2.6 Vent connectors for medium-heat equipment and commercial andindustrial incinerators shall be constructedof factory-built, medium-heat chimneysections or steel of a thickness not less thanthat specified in Table 5-6 and shall complywith the following: [NFPA 54: 12.11.2.6](1) A steel vent connector for equipment

with a vent gas temperature in excess of1,000°F (538°C) measured at theentrance to the connector shall be linedwith medium-duty fire brick (ASTM C64, Specification for Refractories forIncinerators and Boilers, Type F) or theequivalent.

(2) The lining shall be at least 2-1/2 inches(64 mm) thick for a vent connectorhaving a diameter or greatest crosssectional dimension of 18 inches (460mm) or less.

(3) The lining shall be at least 4-1/2 inches(110 mm) thick laid on the 4-1/2 inch(110-mm) bed for a vent connectorhaving a diameter or greatest cross-sectional dimension greater than 18inches (460 mm).

(4) Factory-built chimney sections, ifemployed, shall be joined together inaccordance with the chimney manufac-turer's instructions.

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510.10

TABLE 5-6Minimum Thickness for Steel Vent Connectorsfor Medium-Heat Equipment and Commercial and

Industrial Incinerators[NFPA 54: Table 12.11.2.6]

Vent Connector SizeMinimum

Diameter (in.) Area (in.2) Thickness (in.)Up to 14 Up to 154 0.053Over 14 to 16 154 to 201 0.067Over 16 to 18 201 to 254 0.093Over 18 Larger than 254 0.123

For SI units, 1 in. = 25.4 mm; 1 in.2 = 645 mm2.

510.10.3 Size of Vent Connector.510.10.3.1 A vent connector for gasutilization equipment with a single drafthood or for a Category I fan-assistedcombustion system appliance shall be sizedand installed in accordance with this chapteror other approved engineering methods.[NFPA 54: 12.11.3.1]510.10.3.2 For a single appliance havingmore than one draft hood outlet or fluecollar, the manifold shall be constructedaccording to the instructions of the appliancemanufacturer. Where there are no instruc-tions, the manifold shall be designed andconstructed in accordance with approvedengineering practices. As an alternatemethod, the effective area of the manifoldshall equal the combined area of the flue collarsor draft hood outlets, and the vent connectorsshall have a minimum 1-foot (0.3 m) rise.[NFPA 54: 12.11.3.2]510.10.3.3Where two or more gas appliancesare connected to a common vent or chimney,each vent connector shall be sized in accord-ance with this chapter or other approvedengineering methods. [NFPA 54: 12.11.3.3]As an alternative method applicable onlywhen all of the appliances are draft-hood-equipped, each vent connector shall have aneffective area not less than the area of thedraft hood outlet of the appliance to which itis connected. [NFPA 54: 12.11.3.4]510.10.3.4Where two or more gas appliancesare vented through a common vent connectoror vent manifold, the common vent connec-tor or vent manifold shall be located at thehighest level consistent with available head-

room and clearance to combustible materialand shall be sized in accordance with thischapter or other approved engineeringmethods. [NFPA 54: 12.11.3.5]

As an alternate method applicable onlywhere there are two draft-hood-equippedappliances, the effective area of the commonvent connector or vent manifold and alljunction fittings shall be not less than thearea of the larger vent connector plus 50percent of the areas of smaller flue collaroutlets. [NFPA 54: 12.11.3.6]510.10.3.5 Where the size of a vent connec-tor is increased to overcome installationlimitations and obtain connector capacityequal to the equipment input, the sizeincrease shall be made at the equipmentdraft hood outlet. [NFPA 54: 12.11.3.7]

510.10.4 Two or More Appliances Connectedto a Single Vent.

510.10.4.1 Where two or more ventconnectors enter a common gas vent,chimney flue, or single-wall metal pipe, thesmaller connector shall enter at the highestlevel consistent with the available headroomor clearance to combustible material.[NFPA 54: 12.11.4.1]510.10.4.2 Vent connectors servingCategory I appliances shall not be connectedto any portion of a mechanical draft systemoperating under positive static pressure,such as those serving Category III orCategory IV appliances. [NFPA 54: 12.11.4.2]

510.10.5 Clearance. Minimum clearancesfrom vent connectors to combustible materialshall be in accordance with Table 5-3. [NFPA54: 12.11.5]Exception: The clearance between a ventconnector and combustible material shall bepermitted to be reduced where the com-bustible material is protected as specified forvent connectors in Table 5-4.

510.10.6 Avoid Unnecessary Bends. A ventconnector shall be installed so as to avoid turnsor other construction features that createexcessive resistance to flow of vent gases. [NFPA54: 12.11.6]510.10.7 Joints. Joints between sections ofconnector piping and connections to flue collarsor draft hood outlets shall be fastened inaccordance with one of the following methods:[NFPA 54: 12.11.7](1) By sheet metal screws.


74

Table 5-6 – 510.10

(2) Vent connectors of listed vent material shallbe assembled and connected to flue collarsor draft hood outlets in accordance with themanufacturers' instructions.

(3) Other approved means.510.10.8 Slope. A vent connector shall beinstalled without any dips or sags and shallslope upward toward the vent or chimney atleast 1/4 in./ft. (20 mm/m). [NFPA 54: 12.11.8]Exception: Vent connectors attached to amechanical draft system installed in accordancewith the manufacturers' instructions.

510.10.9 Length of Vent Connector.510.10.9.1 A vent connector shall be asshort as practical and the gas utilizationequipment located as close as practical tothe chimney or vent. [NFPA 54: 12.11.9.1]510.10.9.2 The maximum horizontal lengthof a single-wall connector shall be 75 percentof the height of the chimney or vent exceptfor engineered systems. The maximumlength of an individual connector for achimney or vent system serving multipleappliances, from the appliance outlet to thejunction with the common vent or anotherconnector, shall be 100 percent of the heightof the chimney or vent. [NFPA 54: 12.11.9.2]510.10.9.3 The maximum horizontal lengthof a Type B double-wall connector shall be100 percent of the height of the chimney orvent, except for engineered systems. Themaximum length of an individual connectorfor a chimney or vent system servingmultiple appliances, from the applianceoutlet to the junction with the common ventor another connector, shall be 100 percent ofthe height of the chimney or vent. [NFPA54:12.11.9.3]

510.10.10 Support. A vent connector shall besupported for the design and weight of thematerial employed to maintain clearances andprevent physical damage and separation of joints.[NFPA 54: 12.11.10]510.10.11 Chimney Connection. Whereentering a flue in a masonry or metal chimney,the vent connector shall be installed above theextreme bottom to avoid stoppage. Where athimble or slip joint is used to facilitate removalof the connector, the connector shall be firmlyattached to or inserted into the thimble or slipjoint to prevent the connector from falling out.

Means shall be employed to prevent theconnector from entering so far as to restrict thespace between its end and the opposite wall ofthe chimney flue. [NFPA 54: 12.11.11]510.10.12 Inspection. The entire length of avent connector shall be readily accessible forinspection, cleaning, and replacement. [NFPA54: 12.11.12]510.10.13 Fireplaces. A vent connector shallnot be connected to a chimney flue serving afireplace unless the fireplace flue opening ispermanently sealed. [NFPA 54: 12.11.13]510.10.14 Passage through Ceilings, Floors,or Walls.

510.10.14.1 A vent connector shall not passthrough any ceiling, floor, or fire-resistance-rated wall. A single-wall metal pipeconnector shall not pass through anyinterior wall.Exception: Vent connectors made oflisted Type B or Type L vent materialand serving listed equipment with drafthoods and other equipment listed foruse with Type B gas vents that passthrough walls or partitions constructedof combustible material shall be installedwith not less than the listed clearance tocombustible material.

510.10.14.2 A vent connector made of asingle-wall metal pipe shall not passthrough a combustible exterior wall unlessguarded at the point of passage by aventilated metal thimble not smaller thanthe following: [NFPA 54: 12.11.14.2](1) For listed appliances equipped with

draft hoods and appliances listed foruse with Type B gas vents, the thim-ble shall be a minimum of 4 inches (100mm) larger in diameter than the ventconnector. Where there is a run of notless than 6 feet (1.8 m) of vent connector inthe opening between the draft hoodoutlet and the thimble, the thimble shallbe a minimum of 2 inches (50 mm) largerin diameter than the vent connector.

(2) For unlisted appliances having drafthoods, the thimble shall be a minimumof 6 inches (150 mm) larger in diameterthan the vent connector.

(3) For residential and low-heat appliances,the thimble shall be a minimum of 12

WATER HEATERS 510.10

75

inches (300 mm) larger in diameter thanthe vent connector.Exception: In lieu of thimbleprotection, all combustible materialin the wall shall be removed fromthe vent connector a sufficientdistance to provide the specifiedclearance from such vent connectorto combustible material. Anymaterial used to close up suchopening shall be noncombustible.

510.10.14.3 Vent connectors for medium-heat equipment shall not pass through wallsor partitions constructed of combustiblematerial. [NFPA 54: 12.11.14.3]

510.11 Vent Connectors for Category II,Category III, and Category IV Gas UtilizationEquipment. (See Section 510.4.) [NFPA 54:12.12]510.12 Draft Hoods and Draft Controls.

510.12.1 Equipment Requiring DraftHoods. Vented gas utilization equipmentshall be installed with draft hoods.[NFPA 54: 12.13.1]Exception: Dual oven-type combinationranges; incinerators; direct-ventequipment; fan-assisted combustionsystem appliances; equipment requiringchimney draft for operation; singlefirebox boilers equipped withconversion burners with inputs greaterthan 400,000 Btu/h (117 kW); equipmentequipped with blast, power, or pressureburners that are not listed for use withdraft hoods; and equipment designedfor forced venting.

510.12.2 Installation. A draft hood suppliedwith or forming a part of listed vented gasutilization equipment shall be installedwithout alteration, exactly as furnished andspecified by the equipment manufacturer.[NFPA 54: 12.13.2] If a draft hood is notsupplied by the equipment manufacturerwhere one is required, a drafthood shall be installed, be of a listed orapproved type, and, in the absence of otherinstructions, be of the same size as theequipment flue collar. Where a draft hood isrequired with a conversion burner, it shallbe of a listed or approved type. [NFPA 54:12.13.2.1] Where it is determined that a drafthood of special design is needed orpreferable for a particular installation, the

installation shall be in accordance with therecommendations of the equipmentmanufacturer and shall be with the approvalof the Authority Having Jurisdiction.[NFPA 54: 12.13.2.2]510.12.3 Draft-Control Devices. Where adraft-control device is part of the gasutilization equipment or is supplied by theequipment manufacturer, it shall be installedin accordance with the manufacturer'sinstructions. In the absence of manufacturer'sinstructions, the device shall be attached tothe flue collar of the equipment or as near tothe equipment as practical. [NFPA54: 12.13.3]510.12.4 Additional Devices. Gas utilizationequipment (except incinerators) requiringcontrolled chimney draft shall be permittedto be equipped with a listed double-actingbarometric draft regulator installed andadjusted in accordancewith themanufacturers'instructions. [NFPA 54: 12.13.4]510.12.5 Location. Draft hoods andbarometric draft regulators shall be installedin the same room or enclosure as theequipment in such a manner as to preventany difference in pressure between the hoodor regulator and the combustion air supply.[NFPA 54: 12.13.5]510.12.6 Positioning. Draft hoods anddraft regulators shall be installed in theposition for which they were designedwith reference to the horizontal andvertical planes and shall be located so thatthe relief opening is not obstructed by anypart of the equipment or adjacentconstruction. The equipment and its drafthood shall be located so that the reliefopening is accessible for checking ventoperation. [NFPA 54; 12.13.6]510.12.7 Clearance. A draft hood shall belocated so that its relief opening is not lessthan 6 inches (150 mm) from any surfaceexcept that of the equipment it serves andthe venting system to which the drafthood is connected. Where a greater orlesser clearance is indicated on theequipment label, the clearance shall not beless than that specified on the label. Suchclearances shall not be reduced. [NFPA54:12.13.7]

510.13 Manually Operated Dampers. Amanually operated damper shall not be placedin any equipment vent connector. Fixed baffles


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510.10 – 510.13

shall not be classified as manually operateddampers. [NFPA 54:12.14]510.14 Automatically Operated Vent Dampers.An automatically operated vent damper shallbe of a listed type. [NFPA 54:12.15]510.15 Obstructions. Devices that retard theflow of vent gases shall not be installed in a ventconnector, chimney, or vent. The following shallnot be considered as obstructions: [NFPA54:12.16](1) Draft regulators and safety controls

specifically listed for installation in ventingsystems and installed in accordance with theterms of their listing.

(2) Approved draft regulators and safetycontrols designed and installed in accor-dance with approved engineering methods.

(3) Listed heat reclaimers and automaticallyoperated vent dampers installed inaccordance with the terms of their listing.

(4) Vent dampers serving listed appliancesinstalled in accordance with this chapter orother approved engineering methods.

(5) Approved economizers, heat reclaimers,and recuperators installed in ventingsystems of equipment not required to beequipped with draft hoods, provided thegas utilization equipment manufacturer'sinstructions cover the installation of such adevice in the venting system andperformance in accordance with Sections510.3.1 and 510.3.2 is obtained.

511.0 Sizing of Category I Venting Systems.511.1 These venting tables shall not be used whereobstructions (see Section 510.15) are installed in theventing system. The installation of vents servinglisted appliances with vent dampers shall be inaccordance with the appliance manufacturer’sinstructions or in accordance with the following:[NFPA 54: 13.1.1](1) The maximum capacity of the vent system shall

be determined using the NAT Max column.(2) The minimum capacity shall be determined as

though the appliance were a fan-assistedappliance, using the FAN Min column todetermine the minimum capacity of the ventsystem. Where the corresponding “FANMin” is“NA” the vent configuration shall not be per-mitted and an alternative venting configurationshall be utilized.511.1.1 Where the vent size determined fromthe tables is smaller than the appliance drafthood outlet or flue collar, the use of the smaller

size shall be permitted provided that theinstallation complies with all of the followingrequirements: [NFPA 54: 13.1.2](1) The total vent height (H) is at least 10 feet (3 m).(2) Vents for appliance draft hood outlets or flue

collars 12 inches (300 mm) in diameter orsmaller are not reduced more than one tablesize.

(3) Vents for appliance draft hood outlets or fluecollars larger than 12 inches (300 mm) indiameter are not reduced more than twotable sizes.

(4) The maximum capacity listed in the tablesfor a fan-assisted appliance is reduced by10 percent (0.90 maximum table capacity).

(5) The draft hood outlet is greater than 4 inches(100 mm) in diameter. Do not connect a 3-inch(80mm) diameter vent to a 4-inch (100mm)diameter draft hood outlet. This provisionshall not apply to fan-assisted appliances.

511.1.2 Single-appliance venting configurationswith zero (0) lateral lengths in Tables 5-8, 5-9,and 5-12 shall have no elbows in the ventingsystem. For vent configurations with laterallengths, the venting tables include allowance fortwo 90-degree turns. For each additional elbow upto and including 45 degrees, the maximum capacitylisted in the venting tables shall be reduced by 5percent. For each elbow greater than 45 degreesup to and including 90 degrees, the maximumcapacity listed in the venting tables shall bereduced by 10 percent. [NFPA 54: 13.1.3]511.1.3 Zero (0) lateral (L) shall apply only to astraight vertical vent attached to a top outletdraft hood or flue collar. [NFPA 54: 13.1.4]511.1.4 Sea level input ratings shall be usedwhen determining maximum capacity for high-altitude installation. Actual input (derated foraltitude) shall be used for determining minimumcapacity for high-altitude installation.[NFPA 54: 13.1.5]511.1.5 For appliances with more than oneinput rate, the minimum vent capacity (FANMin) determined from the tables shall be lessthan the lowest appliance input rating, and themaximum vent capacity (FAN Max/NAT Max)determined from the tables shall be greater thanthe highest appliance rating input. [NFPA 54:13.1.6]511.1.6 Listed corrugated metallic chimneyliner systems in masonry chimneys shall besized by using Tables 5-8 or 5-9 for Type B ventswith the maximum capacity reduced by 20 percent(0.80 maximum capacity) and the minimumcapacity as shown in Tables 5-8 or 5-9.Corrugated metallic liner systems installed with


77

bends or offsets shall have their maximumcapacity further reduced in accordance withSection 511.1.2. The 20 percent reduction forcorrugated metallic chimney liner systemsincludes an allowance for one long radius 90-degree turn at the bottom of the liner. [NFPA 54:13.1.7]511.1.7 Where the vertical vent has a largerdiameter than the vent connector, the verticalvent diameter shall be used to determine theminimum vent capacity, and the connectordiameter shall be used to determine themaximum vent capacity. The flow area of thevertical vent shall not exceed seven times theflow area of the listed appliance categorized ventarea, flue collar area, or draft hood outlet areaunless designed in accordance with approvedengineering methods. [NFPA 54: 13.1.9]511.1.8 Connection to Chimney Liners. Connec-tions between chimney liners and listed double-wall connectors shall be made with listed adaptersdesigned for such purposes. [NFPA 54: 13.1.8]511.1.9 Vertical Vent Upsizing 7 x Rule. Wherethe vertical vent has a larger diameter than thevent connector, the vertical vent diameter shall beused to determine the minimum vent capacity, andthe connector diameter shall be used to determinethe maximum vent capacity. The flow area of thevertical vent shall not exceed seven times the flowarea of the listed appliance categorized vent area,flue collar area, or draft hood outlet area unlessdesigned in accordance with approved engineeringmethods. [NFPA 54: 13.1.9]511.1.10 Draft Hood Conversion Accessories.Draft hood conversion accessories for use withmasonry chimneys venting listed Category I fan-assisted appliances shall be listed and installed inaccordance with the listed accessory manu-facturers’ installation instructions. [NFPA 54:13.1.10]511.1.11 Tables 5-8 through 5-12 shall be usedfor chimneys and vents not exposed to theoutdoors below the roof line. A Type B vent orlisted chimney lining system passing through anunused masonry chimney flue shall not beconsidered to be exposed to the outdoors. AType B vent passing through an unventilatedenclosure or chase insulated to a value of notless than R8 shall not be considered to beexposed to the outdoors. Table 5-10 incombination with Table 5-13 shall beused for clay-tile-lined exterior masonrychimneys, provided all of the following are met:[NFPA 54: 13.1.11(1) The vent connector is Type B double wall.(2) The vent connector length is limited to 1-1/2

feet for each inch (180 mm/mm) of vent

connector diameter.(3) The appliance is draft-hood-equipped.(4) The input rating is less than the maximum

capacity given in Table 5-10.(5) For a water heater, the outdoor design

temperature shall not be less than 5°F (15°C).(6) For a space-heating appliance, the input

rating is greater than the minimum capacitygiven by Table 5-13.

(7) Where the conditions of (1) through (6)cannot be met, an alternative venting designshall be used, such as a listed chimneylining system.Exception: Vents serving listed appliancesinstalled in accordance with the applianceinstructions and the terms of the listing.

511.1.12 Corrugated vent connectors shall not besmaller than the listed appliance categorizedvent diameter, flue collar diameter, or drafthood outlet diameter. [NFPA 54: 13.1.12]511.1.13 Vent connectors shall not be upsizedmore than two sizes greater than the listedappliance categorized vent diameter, flue collardiameter, or draft hood outlet diameter. [NFPA54: 13.1.13]511.1.14 In a single run of vent or ventconnector, more than one diameter and typeshall be permitted to be used, provided that allthe sizes and types are permitted by the tables.[NFPA 54: 13.1.14]511.1.15 Interpolation shall be permitted in calcu-lating capacities for vent dimensions that fallbetween table entries. (See Part II-Example G.1.3.)[NFPA 54: 13.1.15]511.1.16 Extrapolation beyond the table entriesshall not be permitted. [NFPA 54: 13.1.16]511.1.17 For vent heights lower than 6 feet andhigher than shown in the tables, engineeringmethods shall be used to calculate vent capacities.[NFPA 54: 13.1.17]

511.2 Additional Requirements to MultipleAppliance Vent Table 5-14 through Table 5-22.

511.2.1 Obstructions and Vent Damper.These venting tables shall not be used whereobstructions (see Section 510.15) are installedin the venting system. The installation of ventsserving listed appliances with vent dampersshall be in accordance with the appliancemanufacturers’ instructions or in accordancewith the following: [NFPA 54: 13.2.1](1) The maximum capacity of the vent

connector shall be determined using theNAT Max column.

(2) The maximum capacity of the vertical vent


78

511.1 – 511.2

or chimney shall be determined using theFAN + NAT column when the secondappliance is a fan-assisted appliance, or theNAT + NAT column when the secondappliance is equipped with a draft hood.

(3) The minimum capacity shall be determinedas if the appliancewere a fan-assisted appliance.(a) The minimum capacity of the vent

connector shall be determined using theFANMin column.

(b) The FAN + FAN column shall be usedwhen the second appliance is a fan-assisted appliance, and the FAN + NATcolumn shall be used when the secondappliance is equipped with a drafthood, to determine whether the verticalvent or chimney configuration is notpermitted (NA). Where the ventconfiguration is NA, the vent configurationshall not be permitted and an alter-native venting configuration shall beutilized.

511.2.2 The maximum vent connector horizontallength shall be 18 in./in. (180 mm/mm) ofconnector diameter as shown in Table 5-7.[NFPA 54: 13.2.2]511.2.3 The vent connector shall be routed tothe vent utilizing the shortest possible route.Connectors with longer horizontal lengths thanthose listed in Table 5-7 are permitted under thefollowing conditions: [NFPA 54: 13.2.3](A) The maximum capacity (FAN Max or NAT

Max) of the vent connector shall be reduced10 percent for each additional multiple ofthe length listed in Table 5-7. For example,the maximum length listed for a 4-inches(100mm) connector is 6 feet (1.8 m). With aconnector length greater than 6 feet (1.8 m) butnot exceeding 12 feet (3.7 m), the maximumcapacity must be reduced by 10 percent(0.90 maximum vent connector capacity).With a connector length greater than 12 feet(3.7 m) but not exceeding 18 feet (5.5 m), themaximum capacity must be reduced by 20percent (0.80 maximum vent capacity).

(B) For a connector serving a fan-assistedappliance, the minimum capacity (FANMin) of the connector shall be determinedby referring to the corresponding singleappliance table. For Type B double-wallconnectors, Table 5-8 shall be used. Forsingle-wall connectors, Table 5-9 shall beused. The height (H) and lateral (L) shall bemeasured according to the procedures for asingle appliance vent, as if the otherappliances were not present.

TABLE 5-7Vent Connector Maximum Length

[NFPA 54: Table 13.2.2]

Connector Diameter Connector HorizontalMaximum (in.) Length (ft.)

3 4-1/24 65 7-1/26 97 10-1/28 129 13-1/210 1512 1814 2116 2418 2720 3022 3324 36

For SI units, 1 in. = 25.4 mm; 1 ft = 0.305 m.[NFPA 54 Table 13.2.2]

511.2.4 Where the vent connectors arecombined prior to entering the vertical portionof the common vent to form a common ventmanifold, the size of the common ventmanifold and the common vent shall bedetermined by applying a 10 percent reduction(.90 x maximum common vent capacity) to theCommon Vent Capacity part of the commonvent tables. The length of the common ventconnector manifold (LM) shall not exceed 18in./in. (180 mm/mm) of common ventconnector manifold diameter (D). (See Part II-Figure G.1(k).) [NFPA 54: 13.2.4]511.2.5 Where the common vertical vent isoffset, the maximum capacity of the commonvent shall be reduced in accordance with Section511.2.6, and the horizontal length of the commonvent offset shall not exceed 18 in./in. (180mm/mm) of common vent diameter. [NFPA 54:13.2.5]511.2.6 For each elbow up to and including 45degrees in the common vent, the maximumcommon vent capacity listed in the ventingtables shall be reduced by 5 percent. Foreach elbow greater than 45 degrees up to andincluding 90 degrees, the maximum commonvent capacity listed in the venting tables shall bereduced by 10 percent. [NFPA 54: 13.2.6]511.2.7 The vent connector capacities listed

WATER HEATERS 511.2

79

in the common vent sizing tables includeallowance for two 90-degree elbows. For eachadditional elbow up to and including 45degrees, the maximum vent connectorcapacity listed in the venting tables shall bereduced by 5 percent. For each elbow greaterthan 45 degrees up to and including 90degrees, the maximum vent connectorcapacity listed in the venting tables shall bereduced by 10 percent. [NFPA 54: 13.2.7]511.2.8 Common Vent Minimum Size. Thecross-sectional area of the common vent shall beequal to or greater than the cross-sectional areaof the largest connector. [NFPA 54:13.2.8]511.2.9 Tee and Wye Fittings. Tee and wyefittings connected to a common vent shall beconsidered as part of the common vent andconstructed of materials consistent with that ofthe common vent. [NFPA 54:13.2.9]511.2.10 At the point where tee or wye fittingsconnect to a common vent, the opening size ofthe fitting shall be equal to the size of thecommon vent. Such fittings shall not beprohibited from having reduced size openings atthe point of connection of appliance ventconnectors. [NFPA 54: 13.2.10]511.2.11 Sea level input ratings shall be usedwhen determining maximum capacity for high-altitude installation. Actual input (derated foraltitude) shall be used for determining minimumcapacity for high-altitude installation. [NFPA 54:13.2.11]511.2.12 The connector rise (R) for eachappliance connector shall be measured from thedraft hood outlet or flue collar to the centerlinewhere the vent gas streams come together.[NFPA 54: 13.2.12]511.2.13 For multiple units of gas utilizationequipment all located on one floor, availabletotal height (H) shall be measured from thehighest draft hood outlet or flue collar up to thelevel of the outlet of the common vent. [NFPA54: 13.2.13]511.2.14 For multistory installations, availabletotal height (H) for each segment of the systemshall be the vertical distance between the highestdraft hood outlet or flue collar entering thatsegment and the centerline of the next higherinterconnection tee. (See Part II-Figure G.1(j).)[NFPA 54: 13.2.14]511.2.15 The size of the lowest connector andof the vertical vent leading to the lowestinterconnection of a multistory system shall bein accordance with Tables 5-8 or 5-9 for availabletotal height (H) up to the lowest interconnection.(See Part II-Figure G.1(n).) [NFPA 54: 13.2.15]

511.2.16 Where used in multistory systems,vertical common vents shall be Type B double-wall and shall be installed with a listed vent cap.[NFPA 54: 13.2.16]511.2.17 Offsets in multistory common ventsystems shall be limited to a single offset in eachsystem, and systems with an offset shall complywith all of the following: [NFPA 54: 13.2.17](1) The offset angle shall not exceed 45 degrees

from vertical.(2) The horizontal length of the offset shall not

exceed 18 inches for each inch (180 mm/mm)of common vent diameter of the segment inwhich the offset is located.

(3) For the segment of the common vertical ventcontaining the offset, the common ventcapacity listed in the common venting tablesshall be reduced by 20 percent (0.80 xmaximumcommon vent capacity).

(4) A multistory common vent shall not bereduced in size above the offset.

511.2.18 Where two or more appliances areconnected to a vertical vent or chimney, the flowarea of the largest section of vertical vent orchimney shall not exceed seven times thesmallest listed appliance categorized vent areas,flue collar area, or draft hood outlet area unlessdesigned in accordance with approvedengineering methods. [NFPA 54: 13.2.18]511.2.19 For appliances with more than oneinput rate, the minimum vent connector capacity(FAN Min) determined from the tables shall beless than the lowest appliance input rating, andthe maximum vent connector capacity (FANMaxor NAT Max) determined from the table shall begreater than the highest appliance input rating.[NFPA 54: 13.2.19]511.2.20 Listed corrugated metallic chimneyliner systems in masonry chimneys shall besized by using Tables 5-14 or 5-15 for Type Bvents, with the maximum capacity reduced by20 percent (0.80 maximum capacity) and theminimum capacity as shown in Tables 5-14 or5-15. Corrugated metallic liner systemsinstalled with bends or offsets shall have theirmaximum capacity further reduced in accordancewith Sections 511.2.5 and 511.2.6. The 20percent reduction for corrugated metallicchimney liner systems includes an allowancefor one long radius 90-degree turn at thebottom of the liner. [NFPA 54: 13.2.20]511.2.21 Tables 5-14 and 5-15 shall be used forchimneys and vents not exposed to the outdoorsbelow the roof line. A Type B vent passing


80

511.2

through an unventilated enclosure or chaseinsulated to a value of not less than R8 shall notbe considered to be exposed to the outdoors.Tables 5-19 and 5-20 shall be used for clay-tile-lined exterior masonry chimneys, provided all ofthe following conditions are met: [NFPA54:13.2.22](1) Vent connector is Type B double-wall.(2) At least one appliance is draft-hood-

equipped.(3) The combined appliance input rating is less

than the maximum capacity given by Table5-19 (for NAT + NAT) or Table 5-21 (forFAN + NAT).

(4) The input rating of each space-heatingappliance is greater than the minimuminput rating given by Table 5-20 (forNAT + NAT) or Table 5-21 (for FAN +NAT).

(5) The vent connector sizing is in accordancewith Table 5-16.

(6) Where these conditions cannot be met, analternative venting design shall be used,such as a listed chimney lining system.Exception: Vents serving listed appliancesinstalled in accordance with the appliancemanufacturers’ installation instructions.

511.2.22 Vent connectors shall not be increasedmore than two sizes greater than the listedappliance categorized vent diameter, flue collardiameter, or draft hood outlet diameter. Ventconnectors for draft-hood-equipped appliancesshall not be smaller than the draft hood outletdiameter. Where vent connector sizes determinedfrom the tables for fan-assisted appliances aresmaller than the flue collar diameter, the use ofthe smaller sizes shall be permitted providedthat the installation complies with all of thefollowing conditions: [NFPA 54: 13.2.24](1) Vent connectors for fan-assisted appliance

flue collars 12 inches (300 mm) in diameteror smaller are not reduced by more than onetable size [e.g., 12 inches to 10 in. (300 mm to250 mm) is a one-size reduction] and thoselarger than 12 inches (300 mm) in diameterare not reduced more than two table sizes[e.g., 24 inch to 20 inch (610 mm to 510 mm)is a two-size reduction].

(2) Fan-assisted appliances are common ventedwith a draft-hood-equipped appliance.

(3) The vent connector has a smooth interior wall.511.2.23 All combinations of pipe sizes,single-wall, and double-wall metal pipeshall be allowed within any connector runor within the common vent, provided ALL

of the appropriate tables permit ALL of thedesired sizes and types of pipe, as if theywere used for the entire length of the subjectconnector or vent. Where single-wall andType B double-wall metal pipes are used forvent connectors within the same ventingsystem, the common vent must be sizedusing Tables 5-15 or 5-17 as appropriate.[NFPA 54: 13.2.25]

511.2.24 Where a table permits more than onediameter of pipe to be used for a connector orvent, all the permitted sizes shall be permitted tobe used. [NFPA 54: 13.2.26]511.2.25 Interpolation shall be permitted incalculating capacities for vent dimensions thatfall between table entries. (See Part II Annex G.1.3.)[NFPA 54: 13.2.27]511.2.26 Extrapolation beyond the tableentries shall not be permitted. [NFPA 54: 13.2.28]511.2.27 For vent heights lower than 6 feet andhigher than shown in the tables, engineeringmethods shall be used to calculate vent capacities.[NFPA 54: 13.2.28]

512.0 Direct-Vent Equipment. Listed direct-ventgas utilization equipment shall be consideredproperly vented where installed in accordance withthe terms of its listing, the manufacturers'instructions, and Section 510.8.3. [NFPA 54: 12.3.5]

WATER HEATERS 511.2 – FIgure 5-7

81

FIGURE 5-7 All Combustion Air from IndoorSpaces through Indoor Combustion AirOpenings. [NFPA 54: Figure A.9.3.2.3(1)]


82

Figure 5-8 – Figure 5-11

FIGURE 5-8 All Combustion Air from Outdoors -Inlet Air from Ventilated Crawl Space and OutletAir to Ventilated Attic. [NFPA 54: FigureA.9.3.3.1(a)]

FIGURE 5-10 All Combustion Air from Outdoorsthrough Horizontal Ducts. [NFPA 54: FigureA.9.3.3.1(2)]

FIGURE 5-9 All Combustion Air from Outdoorsthrough Ventilated Attic. [NFPA 54: FigureA.9.3.3.1(1)(b)]

FIGURE 5-11 All Combustion Air from Outdoorsthrough Single Combustion Air Opening.[NFPA 54: Figure A.9.3.3.2]

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Figure 5-12 – Figure 5-13

FIGURE 5-12 Exit Terminals of Mechanical Draft and Direct-Vent Venting Systems. [NFPA 54: Figure A.12.9]

FIGURE 5-13 Range of Winter Design Temperatures Used in Analyzing Exterior Masonry Chimneys inthe United States.


84

Table 5-8

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85

Table 5-8 continued


86

Table 5-9

WATER HEATERS

87

Table 5-10


88

Table 5-11

WATER HEATERS

89

Table 5-12


90

Table 5-13

WATER HEATERS

91

Table 5-14


92

Table 5-14 continued

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93

Table 5-15


94

Table 5-16

WATER HEATERS

95

Table 5-17


96

Table 5-18 – Table 5-19

WATER HEATERS

97

Table 5-20


98

Table 5-21

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99

Table 5-22


100

Figure G.1(a) – G.1(d)

PART II

This is originally from NFPA 54,which contains additional references from the UPC.

Sizing of Venting Systems Serving AppliancesEquipped with Draft Hoods, Category IAppliances, and Appliances Listed for Usewith Type B Vents

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Figure G.1(e) – G.1(h)


102

Table G.1(i) – Table G.1(l)

G.1.1 Example 1: Single Draft-Hood-EquippedAppliance. An installer has a 120,000-Btu/h inputappliance with a 5-inch diameter draft hood outletthat needs to be vented into a 10-foot-high Type Bvent system. What size vent should be used assuming(1) a 5-foot lateral single-wall metal vent connector isused with two 90-degree elbows or (2) a 5-foot lateralsingle-wall metal vent connector is used with three 90-degree elbows in the vent system? See Figure G.1.1.

SolutionTable 5-9 should be used to solve this problembecause single-wall metal vent connectors are beingused with a Type B vent, as follows:

(1) Read down the first column in Table 5-9 until therow associated with a 10-foot height and 5-footlateral is found. Read across this row until avent capacity greater than 120,000 Btu/h islocated in the shaded columns labeled NAT Maxfor draft-hood-equipped appliances. In this case,a 5-inch-diameter vent has a capacity of 122,000Btu/h and can be used for this application.

(2) If three 90-degree elbows are used in the ventsystem, the maximum vent capacity listed in thetables must be reduced by 10 percent (see NFPA54:13.1.3). This implies that the 5-inch-diametervent has an adjusted capacity of only 110,000

Btu/h. In this case, the vent system must beincreased to 6 inches in diameter. See thefollowing calculations:

122,000 x 0.90 = 110,000 for 5-inch ventFrom Table 5-10, select 6-inch vent.186,000 x 0.90 = 167,000

This figure is greater than the required120,000. Therefore, use a 6-inch vent andconnector where three elbows are used.

G.1.2. Example 2: Single Fan-Assisted Appliance.An installer has an 80,000 Btu/h input fan-assistedappliance that must be installed using 10 feet oflateral connector attached to a 30-foot high Type Bvent. Two 90 -degree elbows are needed for theinstallation. Can a single-wall metal vent connectorbe used for this application? See Figure G.1.2.

SolutionTable 5-10 refers to the use of single-wall metal ventconnectors with Type B vent. In the first columnfind the row associated with a 30-foot height and a10-foot lateral. Read across this row, looking at the

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G.1.1 – G 1.2

FAN Min and FAN Max columns, to find that a 3-inch diameter single-wall metal vent connector is notrecommended. Moving to the next larger size single-wall connector (4 inch), we find that a 4-inchdiameter single-wall metal connector has arecommended maximum vent capacity of 144,000Btu/h. The 80,000 Btu/h fan-assisted appliance isoutside this range, so the conclusion is that a single-wall metal connector could be used to vent theappliance. Table 5-9 shows the acceptable range ofvent capacities for a 4 inch vent with 5 feet of lateralto be between 72,000 Btu/h and 157,000 Btu/h.

If the appliance cannot be moved closer to thevertical vent, then a Type B vent could be used as theconnector material. In this case, Table 5-8 showsthat, for a 30-foot-high vent with 10 feet of lateral,the acceptable range of vent capacities for a 4-inch-diameter vent attached to a fan-assisted appliance isbetween 37,000 Btu/h and 150,000 Btu/h.

G.1.3. Example 3: Interpolating Between Table Values.An installer has an 80,000 Btu/h input appliance witha 4-inch diameter draft hood outlet that needs to bevented into a 12-foot-high Type B. Can this appliancebe vented using a 4-inch diameter vent?

SolutionTable 5-8 is used in the case of an all Type B Ventsystem. However, since there is no entry in Table 5-8for a height of 12 feet, interpolation must be used.Read down the 4-inch diameter NAT Max column tothe row associated with a 10-foot height and 5-footlateral to find the capacity value of 77,000 Btu/h.Read further down to the 15-foot height, 5-footlateral row to find the capacity value of 87,000Btu/h. The difference between the 15-foot heightcapacity value and the 10-foot height capacity valueis 10,000 Btu/h. The capacity for a vent system witha 12-foot height is equal to the capacity for a 10-footheight plus 2/5 of the difference between the 10-footand 15-foot height values, or 77,000 + 2/5 x 10,000 =81,000 Btu/h. Therefore, a 4-inch diameter vent canbe used in the installation.

G.2 Examples Using Common Venting Tables.

G.2.1 Example 4: Common Venting Two Draft-Hood-Equipped Appliances. A 35,000-Btu/h water heater isto be common vented with a 150,000 Btu/h furnace,using a common vent with a total height of 30 feet.The connector rise is 2 feet for the water heater with ahorizontal length of 4 feet. The connector rise for thefurnace is 3 feet with a horizontal length of 8 feet.Assume single-wall metal connectors will be usedwith Type B vent. What size connectors andcombined vent should be used in this installation?


104

G.1.2 – G.2.1

See Figure G.2.1.

SolutionTable 5-15 should be used to size single-wall

metal vent connectors attached to Type B verticalvents. In the Vent Connector Capacity portion ofTable 5-15, find the row associated with a 30-footvent height. For a 2-foot rise on the vent connectorfor the water heater, read the shaded columns fordraft-hood-equipped appliances to find that a 3-inchdiameter vent connector has a capacity of 37,000Btu/h. Therefore, a 3-inch single-wall metal ventconnector can be used with the water heater. For adraft-hood-equipped furnace with a 3-foot rise, readacross the appropriate row to find that a 5-inch-diameter vent connector has a maximum capacity of120,000 Btu/h (which is too small for the furnace),and a 6-inch diameter vent connector has amaximum vent capacity of 172,000 Btu/h. Therefore,a 6-inch diameter vent connector should be usedwith the 150,000 Btu/h furnace. Since both ventconnector horizontal lengths are less than themaximum lengths listed in Table 5-8, the table valuescan be used without adjustments.

In the Common Vent Capacity portion of Table5-15, find the row associated with a 30-foot ventheight and read over to the NAT + NAT portion ofthe 6-inch diameter column to find a maximumcombined capacity of 257,000 Btu/h. Since the twoappliances total only 185,000 Btu/h, a 6-inchcommon vent can be used.

G.2.2 Example 5 (a): Common Venting a Draft-Hood-Equipped Water Heater with a Fan-AssistedFurnace into a Type B Vent. In this case, a 35,000-Btu/h input draft-hood-equipped water heater with a4-inch diameter draft hood outlet, 2-feet of connectorrise, and 4-feet of horizontal length is to be commonvented with a 100,000 Btu/h fan-assisted furnacewith a 4-inch diameter flue collar, 3-feet of connectorrise, and 6-feet of horizontal length. The commonvent consists of a 30-foot height of Type B vent. Whatare the recommended vent diameters for eachconnector and the common vent? The installer wouldlike to use a single-wall metal vent connector. SeeFigure G.2.2.

Solution (See Table 5-15)Water Heater Vent Connector Diameter. Since

the water heater vent connector horizontal length of4 feet is less than the maximum value listed in Table5-15, the venting table values can be used withoutadjustment. Using the Vent Connector Capacityportion of Table 5-15, read down the Total VentHeight (H) column to 30 feet and read across the 2-feet Connector Rise (R) row to the first Btu/h rating

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G.2.1 – G.2.2

TABLE G.2.3Masonry Chimney Liner Dimensions with Circular

Equivalents

InsideInside Diameter

Nominal Dimensions or Equivalent EquivalentLiner Size of Liner Diameter Area(in.) (in.) (in.) (in.2)4 x 8 2-1/2 x 6-1/2 4.0 12.2

5.0 19.66.0 28.37.0 38.3

8 x 8 6-3/4 x 6-3/4 7.4 42.78.0 50.3

8 x 12 6-1/2 x 10-1/2 9.0 63.610.0 78.5

12 x 12 9-3/4 x 9-3/4 10.4 83.311.0 95.0

12 x 16 9-1/2 x 13-1/2 11.8 107.512.0 113.014.0 153.9

16 x 16 13-1/4 x 13-1/4 14.5 162.915.0 176.7

16 x 20 13 x 17 16.2 206.118.0 254.4

20 x 20 16-1/2 x 16-3/4 18.2 260.220.0 314.1

20 x 24 16-1/2 x 20-1/2 20.1 314.222.0 308.1

24 x 24 20-1/4 x 20-1/4 22.1 308.124.0 452.3

24 x 28 20-1/4 x 24-1/4 24.1 456.228 x 28 24-1/4 x 24-1/4 26.4 543.3

27.0 572.530 x 30 25-1/2 x 25-1/2 27.9 607.030 x 36 25-1/2 x 31-1/2 30.9 749.9

33.0 855.336 x 36 31-1/2 x 31-1/2 34.4 929.4

36.0 1017.9For SI units, 1 in. = 25.4 mm, 1 in.2 = 645 mm2.Note: When liner sizes differ dimensionally from those shown in thistable, equivalent diameters can be determined from published tables forsquare and rectangular ducts of equivalent carrying capacity or byother engineering methods.

in the NAT Max column that is equal to or greaterthan the water heater input rating. The table showsthat a 3-inch vent connector has a maximum inputrating of 37,000 Btu/h. Although this rating isgreater than the water heater input rating, a 3-inchvent connector is prohibited by Section 511.2.18. A 4-inch vent connector has a maximum input rating of67,000 Btu/h and is equal to the draft hood outletdiameter. A 4-inch vent connector is selected. Sincethe water heater is equipped with a draft hood, thereare no minimum input rating restrictions.

Furnace Vent Connector Diameter. Using the VentConnector Capacity portion of Table 5-15, read downthe Total Vent Height (H) column to 30 feet andacross the 3-foot Connector Rise (R) row. Since thefurnace has a fan-assisted combustion system, findthe first FAN Max column with a Btu/h ratinggreater than the furnace input rating. The 4-inchvent connector has a maximum input rating of119,000 Btu/h and a minimum input rating of 85,000Btu/h.

The 100,000-Btu/h furnace in this example fallswithin this range, so a 4-inch connector is adequate.Since the furnace vent connector horizontal length of6 feet is less than the maximum value listed in Table5-8, the venting table values can be used withoutadjustment. If the furnace had an input rating of80,000 Btu/h, then a Type B vent connector would beneeded in order to meet the minimum capacity limit.(see Table 5-14)

Common Vent Diameter. The total input to thecommon vent is 135,000 Btu/h. Using the CommonVent Capacity portion of Table 5-15, read down theVent Height (H) column to 30 feet and across thisrow to find the smallest vent diameter in the FAN +NAT column that has a Btu/h rating equal to orgreater than 135,000 Btu/h. The 4-inch commonvent has a capacity of 132,000 Btu/h and the 5-inchcommon vent has a capacity of 202,000 Btu/h.Therefore, the 5-inch common vent should be used inthis example.Summary: In this example, the installer can use a 4-inch diameter, single-wall metal vent connector forthe water heater and a 4-inch-diameter, single-wallmetal vent connector for the furnace. The commonvent should be a 5-inch-diameter Type B vent.

G.2.3 Example 5 (b): Common Venting into anInterior Masonry Chimney. In this case, the waterheater and fan-assisted furnace of Example 5 (a) areto be common-vented into a clay-tile-lined masonrychimney with a 30-foot height. The chimney is notexposed to the outdoors below the roof line. Theinternal dimensions of the clay tile liner arenominally 8 inches x 12 inches. Assuming the samevent connector heights, laterals, and materials found

in example 5 (a), what are the recommended ventconnector diameters, and is this an acceptableinstallation?SolutionTable 5-17 is used to size common ventinginstallations involving single-wall connectors intomasonry chimneys.

Water Heater Vent Connector Diameter. UsingTable 5-17, Vent Connector Capacity, read down theVent Height (H) column to 30 feet, and read acrossthe 2-foot Connector Rise (R) row to the first Btu/hrating in the NAT Max column that is equal to orgreater than the water heater input rating. The tableshows that a 3-inch vent connector has a maximuminput of only 31,000 Btu/h, while a 4-inch ventconnector has a maximum input of 57,000 Btu/h. A4-inch vent connector must therefore be used.

Furnace Vent Connector Diameter. Using the VentConnector Capacity portion of Table 5-17, read downthe total Vent Height (H) column to 30 feet andacross the 3-feet Connector Rise (R) row. Because thefurnace has a fan-assisted combustion system, findthe first FAN Max column with a Btu/h ratinggreater than the furnace input rating. The 4-inch ventconnector has a maximum input rating of 127,000Btu/h and a minimum input rating of 95,000 Btu/h.The 100,000 Btu/h furnace in this example fallswithin this range, so a 4-inch connector is adequate.

Masonry Chimney. From Table G.2.3, theequivalent area for a nominal liner size of 8 inches x12 inches is 63.6 inches2. Using Table 5-17, CommonVent Capacity, read down the FAN + NAT columnunder the Minimum Internal Area of Chimney valueof 63 to the row for 30-foot height to find a capacityvalue of 739,000 Btu/h. The combined input ratingof the furnace and water heater, 135,000 Btu/h, isless than the table value so this is an acceptableinstallation.Section 511.2.4 requires the common vent area to beno greater than seven times the smallest listedappliance categorized vent area, flue collar area, ordraft hood outlet area. Both appliances in thisinstallation have 4-inch-diameter outlets. From TableG.2.3, the equivalent area for an inside diameter of 4-inch is 12.2 in.2. Seven times 12.2 equals 85.4, which isgreater than 63.6, so this configuration is acceptable.

G.2.4 Example 5 (c): Common Venting into anExterior Masonry Chimney. In this case, the waterheater and fan-assisted furnace of Examples 5(a) and5(b) are to be common-vented into an exteriormasonry chimney. The chimney height, clay-tile-liner dimensions, and vent connector heights andlaterals are the same as in Example 5(b). This systemis being installed in Charlotte, North Carolina. Doesthis exterior masonry chimney need to be relined? If


106

G.2.2 – G.2.4

so, what corrugated metallic liner size isrecommended? What vent connector diameters arerecommended? See Table G.2.3 and Figure 5-14.Solution

According to 13.2.18, Type B vent connectors arerequired to be used with exterior masonry chimneys.Use Table 5-21(a) and Table 5-21(b) to sizeFAN+NAT common venting installations involvingType-B double-wall connectors into exteriormasonry chimneys.

The local 99 percent winter design temperatureneeded to use Table 5-21(a) and Table 5-21(b) can befound in the ASHRAE Handbook – Fundamentals. ForCharlotte, North carolina, this design temperature is 19˚F.

Chimney Liner Requirement. As in Example 5 (b),use the 63 in.2 column of Table 5-21(a) to the 30 ftheight row to find that the combined appliancemaximum input is 747,000 Btu/h. The combinedinput rating of the appliance in this installation,135,000 Btu/h, is less than the maximum value, sothis criterion is satisfied. Table 5-21(b), at a 19˚Fdesign temperature, and at the same vent height andinternal area used earlier, shows that the minimumallowable input rating of a space-heating appliance is470,000 Btu/h. The furnace input rating of 100,000Btu/h is less than this minimum value. So thiscriterion is not satisfied, and an alternative ventingdesign needs to be used, such as a Type B ventshown in Example 5(a) or a listed chimney linersystem shown in the rest of the example.

According to Section 511.1.6, Table 5-9 or Table5-10 are used for sizing corrugated metallic liners inmasonry chimneys, with the maximum commonvent capacities reduced by 20 percent. This examplewill be continued assuming Type B vent connectors.

Water Heater Vent Connector Diameter. UsingTable 5-14 Connector Capacity, read down the totalVent Height (H) column to 30 feet, and read acrossthe 2-foot Connector Rise (R) row to the firstBtu/hour rating in the NAT Max column that isequal to or greater than the water heater inputrating. The table shows that a 3 in. vent connectorhas a maximum capacity of 39,000 Btu/h. Althoughthis rating is greater than the water heater inputrating, a 3-inch vent connector is prohibited by511.1.6. A 4 in. vent connector has a maximum inputrating of 70,000 Btu/h and is equal to the draft hoodoutlet diameter. A 4-inch vent connector is selected.

Furnace Vent Connector Diameter. Using Table 5-14, Vent Connector Capacity, read down the totalVent Height (H) column to 30 feet, and read acrossthe 3-foot Connector Rise (R) row to the first Btu/hrating in the FAN MAX column that is equal to orgreater than the furnace input rating. The 100,000Btu/h furnace in this example falls within this range,so a 4-inch connector is adequate.

Chimney Liner Diameter. The total input to thecommon vent is 135,000 Btu/h. Using the CommonVent Capacity portion of Table 5-14, read down thetotal Vent Height (H) column to 30 feet and acrossthis row to find the smallest vent diameter in theFAN + NAT column that has a Btu/h rating greaterthan 135,000 Btu/h. The 4 in. common vent has acapacity of 138,000 Btu/h. Reducing the maximumcapacity by 20 percent (see 13.2.19) results in amaximum capacity for a 4-inch corrugated liner of110,000 Btu/h, less than the total input of 135,000Btu/h. So a larger liner is needed. The 5-inchcommon vent capacity listed in Table 5-14 is 210,000Btu/h, and after reducing by 20 percent is 168,000Btu/h. Therefore, a 5-inch corrugated metal linershould be used in this example.

Single Wall Connectors. Once it has beenestablished that relining the chimney is necessary,Type B double-wall vent connectors are notspecifically required. This example could be redoneusing Table 5-15 for single-wall vent connectors. Forthis case, the vent connector and liner diameterswould be the same as found for Type B double-wallconnectors.

The following is originally from NFPA 54, whichcontains additional reference.

Example of Combination of Indoor and OutdoorCombustion and Ventilation Opening Design.

J.1 Example of Combination Indoor and OutdoorCombustion Air Opening. Determine the requiredcombination of indoor and outdoor combustion airopening sizes for the following equipmentinstallation example.

Example Installation: A fan-assisted furnace and adraft-hood-equipped water heater with the followinginputs are located in a 15-foot x 30-foot basementwith an 8-foot ceiling. No additional indoor spacescan be used to help meet the equipment combustionair needs.

Fan-Assisted Furnace Input: 100,000 Btu/hDraft-Hood-Equipped Water Heater Input:40,000 Btu/h

Solution

(1) Determine the total available room volume:Equipment room volume: 15 feet x 30 feet with an8-foot ceiling = 3,600 feet3

(2) Determine the total required volume: The standardmethod to determine combustion air will beused to calculate the required volume.The combined input for the appliances located in

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G.2.4

the basement is calculated as follows:100,000 Btu/h +40,000 Btu/h = 140,000 Btu/hThe Standard Method requires that the requiredvolume be determined based on 50 cubic feet per1,000 Btu/hour. Using Table A.9.3.2.1, therequired volume for a 140,000 Btu/h waterheater is 7,000 feet3.

Conclusion: Indoor volume is insufficient tosupply combustion air since the total of 3,600 feet3does not meet the required volume of 7000 feet3.Therefore, additional combustion air must beprovided from the outdoors.

(3) Determine ratio of the available volume to therequired volume:

3,600 ft.3 = 0.517000 ft.3

(4) Determine the reduction factor to be used toreduce the full outdoor air opening size to theminimum required based on ratio of indoorspaces:1.00 – 0.51 (from Step 3) = 0.49

(5) Determine the single outdoor combustion airopening size as if all combustion air is to comefrom outdoors. In this example, the combustionair openingdirectly communicateswith the outdoors.

140,000 Btu/h= 47 in.23,000 Btu/in.2

(6) Determine the minimum outdoor combustionair opening area:Outdoor opening area = 0.49(from Step 4) x 47 in.2= 23 in.2

Section 507.3 requires the minimum dimension of theair opening should not be less than 3 inches.


108

G.2.4

Appliance Input(Btu/h)

5,00010,00015,00020,00025,00030,00035,00040,00045,00050,00055,00060,00065,00070,00075,00080,00085,00090,00095,000100,000105,000110,000115,000120,000125,000130,000135,000140,000145,000150,000160,000170,000180,000190,000200,000210,000220,000230,000240,000250,000260,000270,000280,000290,000300,000

Required Volume(ft.3)

2505007501,0001,2501,5001,7502,0002,2502,5002,7503,0003,2503,5003,7504,0004,2504,5004,7505,0005,2505,5005,7506,0006,2506,5006,7507,0007,2507,5008,0008,5009,0009,50010,00010,50011,00011,50012,00012,50013,00013,50014,00014,50015,000

TABLE A.9.3.2.1Standard Method Volume, All Appliances

507.4.1 See Figure 5-8 • 507.4.1(1) See Figure 5-9 andFigure 5-10 • 507.4.1(2) See Figure 5-11 • 507.4.2 SeeFigure 5-12 • For information on gas convenienceoutlets, see AGA 7-90, Requirements for Gas ConvenienceOutlets.

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California Plumbing Code

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